Generate # Extended help with all component descriptions

[MilesCranmer]

This adds an automatically-generated # Extended help section with all component descriptions.

This won't appear in the normal docs for ?, only for ?? which is the extended help, as described in #46.

Using my package's NodeInterface as an example, here is the before:

(Expand)

'''
    NodeInterface
'''

An Interfaces.jl `Interface` with mandatory components `(:create_node, :copy, :hash, :any, :equality, :preserve_sharing, :constructorof, :eltype, :with_type_parameters, :default_allocator, :set_node!, :count_nodes, :tree_mapreduce)` and optional components `(:leaf_copy, :leaf_hash, :leaf_equal, :branch_copy, :branch_hash, :branch_equal, :count_depth, :is_node_constant, :count_constants, :filter_map, :has_constants, :get_constants, :set_constants!, :index_constants, :has_operators)`.

Defines the interface for [`AbstractExpressionNode`](@ref) which can include various operations such as copying, hashing, and checking equality, as well as tree-specific operations like map-reduce and node manipulation.

And the after:

'''
    NodeInterface
'''

An Interfaces.jl `Interface` with mandatory components `(:create_node, :copy, :hash, :any, :equality, :preserve_sharing, :constructorof, :eltype, :with_type_parameters, :default_allocator, :set_node!, :count_nodes, :tree_mapreduce)` and optional components `(:leaf_copy, :leaf_hash, :leaf_equal, :branch_copy, :branch_hash, :branch_equal, :count_depth, :is_node_constant, :count_constants, :filter_map, :has_constants, :get_constants, :set_constants!, :index_constants, :has_operators)`.

Defines the interface for [`AbstractExpressionNode`](@ref) which can include various operations such as copying, hashing, and checking equality, as well as tree-specific operations like map-reduce and node manipulation.

# Extended help

## Mandatory keys:

  * `create_node`: creates a new instance of the node type
  * `copy`: returns a copy of the tree
  * `hash`: returns the hash of the tree
  * `any`: checks if any element of the tree satisfies a condition
  * `equality`: checks equality of the tree with itself and its copy
  * `preserve_sharing`: checks if the node type preserves sharing
  * `constructorof`: gets the constructor function for a node type
  * `eltype`: gets the element type of the node
  * `with_type_parameters`: applies type parameters to the node type
  * `default_allocator`: gets the default allocator for the node type
  * `set_node!`: sets the node's value
  * `count_nodes`: counts the number of nodes in the tree
  * `tree_mapreduce`: applies a function across the tree

## Optional keys:

  * `leaf_copy`: copies a leaf node
  * `leaf_hash`: computes the hash of a leaf node
  * `leaf_equal`: checks equality of two leaf nodes
  * `branch_copy`: copies a branch node
  * `branch_hash`: computes the hash of a branch node
  * `branch_equal`: checks equality of two branch nodes
  * `count_depth`: calculates the depth of the tree
  * `is_node_constant`: checks if the node is a constant
  * `count_constants`: counts the number of constants
  * `filter_map`: applies a filter and map function to the tree
  * `has_constants`: checks if the tree has constants
  * `get_constants`: gets constants from the tree, returning a tuple of: (1) a flat vector of the constants, and (2) a reference object that can be used by `set_constants!` to efficiently set them back
  * `set_constants!`: sets constants in the tree, given: (1) a flat vector of constants, (2) the tree, and (3) the reference object produced by `get_constants`
  * `index_constants`: indexes constants in the tree
  * `has_operators`: checks if the tree has operators

For multiple methods, it generates a nested list.

For example, for the GroupInterface:

'''
    GroupInterface
'''

An Interfaces.jl `Interface` with mandatory components `(:neutral_check, :multiplication_check, :inversion_check)` and optional components `()`.

A group is a set of elements with a neutral element where you can perform multiplications and inversions.

The conditions checking the interface accept an `Arguments` object with two fields named `x` and `y`. The type of the first field `x` must be the type you wish to declare as implementing `GroupInterface`.

# Extended help

## Mandatory keys:

  * `neutral_check`:

      * neutral stable
  * `multiplication_check`:

      * multiplication stable
  * `inversion_check`:

      * inversion stable
      * inversion works

[rafaqz]

Thanks, looks good. Let's just mark these new methods as internal

[rafaqz]

Maybe run the Base interfaces.jl test manually to see what's broken. Some may not have descriptions? (and that's allowed)

[MilesCranmer]

Oh yeah it looks like it's the fact that some keys don't have descriptions. I'll make a patch.

[MilesCranmer]

Ok it is done. I also refactored things a bit nicer and made it more robust to any future edge cases

[MilesCranmer]

Ok I fixed the docs build by just splitting out the test into a separate file and including in a line with #src

julia --project=docs/ docs/make.jl
[ Info: generating markdown page from `~/PermaDocuments/Interfaces.jl/test/basic.jl`
[ Info: writing result to `~/PermaDocuments/Interfaces.jl/docs/src/basic.md`
[ Info: generating markdown page from `~/PermaDocuments/Interfaces.jl/test/advanced.jl`
[ Info: writing result to `~/PermaDocuments/Interfaces.jl/docs/src/advanced.md`
[ Info: SetupBuildDirectory: setting up build directory.
[ Info: Doctest: running doctests.
[ Info: ExpandTemplates: expanding markdown templates.
[ Info: CrossReferences: building cross-references.
[ Info: CheckDocument: running document checks.
[ Info: Populate: populating indices.
[ Info: RenderDocument: rendering document.
[ Info: HTMLWriter: rendering HTML pages.
[ Info: Automatic `version="0.3.0"` for inventory from ../Project.toml
┌ Warning: Documenter could not auto-detect the building environment. Skipping deployment.
└ @ Documenter ~/.julia/packages/Documenter/qoyeC/src/deployconfig.jl:76