Local preferences file

[naholyr]

This PR references Issue #115.

Add support for a .ender.json file, that will store default values for CLI options.

Example content:

{
  "output": "./public/js"
, "noop": true
}

Then ender build backbone will be the same as ender build --output ./public/js --noop backbone.

Note: "output" and "use" are idempotent. If you specify "output", but not "use" (or "use" but not "output") then both options will be defined with the specified value.

[naholyr]

Any chance this request would be discussed ? :-)

[rvagg]

For what it's worth I think this is great!

[rvagg]

Closing this because we're focusing dev on the 1.0-wip branch. I'm rolling requests for a config file into #131 and, feel free to discuss there.