`maximumLineLength` - rewrite `functionSignature` handling, include `FunctionExpression`

[himdel]

This closes #2032 - maximumLineLength allExcept: ['functionSignature'] - broken in IIFE.

I've essentially rewritten the functionSignature handling to use iterateNodesByType instead of the recursive searchBodyForDecl, and include FunctionExpression (as well as the previously checked FunctionDeclaration and MethodDefiniton)

Also abstracted common boilerplate into a local removeLoc function - the empty lines .loc.start.line - 1 through .loc.end.line - 1 logic is used in multiple places there and warrants a helper.

Spec changes:

• add should not report functions within IIFE blocks
• change: should to should not in .. report functions stored in variables
• extended that same spec to test for multiple variations - var, let or const, with or without parameters or name
• add should report functions within comments - that one mostly so that we verify at least something can fail (which may previously have been the job of should report functions stored in variables)

[himdel]

.. Also added support for ArrowFunctionExpression, so now even fooooooooooo => baaaaaaaaar is ignored.

[markelog]

Coverage decreased (-0.001%) to 99.327%

?

Also, would you mind adding example for this param?

[himdel]

Coverage is decreased because 100% of shorter code is less code covered than 100% of longer code , apparently :).

Also, would you mind adding example for this param?

Sure, will do..

[himdel]

..added a few examples..

[markelog]

Thank you!