Standardize on a way to pass go/no-go flags to hooks

[eddyystop]

+## Cancelling hook chain
+
+If you want certain hooks to be skipped you may set any custom property onto context, then wrap hooks you want to skip
+into iff-hook and check.
+> Note: The aforementioned trick doesn't prevent database call. In this case context.result should be set in before hook.
+
+```js
+const { iff } = require('feathers-hooks-common');
+
+app.service('servicename').hooks({

• before: [
• context => {

•  context.cancelled = true;
  

•  return context;
  

• },
• iff(

•  context => context.cancelled,
  

•  [hookA, hookB] // <- skipped
  

• ),
• hookC // not skipped
• ]
  +})
  +```

[eddyystop]

Feathers hooks now implements SKIP.