Support applying aspects to MapLike objects

[kitsonk]

aspect now supports applying advice to Map like objects (e.g. ones that utilise key value pairs using a .set() and .get() functionality).

This is to support allowing Maps to be used when keeping a map of listeners, thereby supporting dojo/compose#52.

Also, this PR cleans up aspect to align it to current coding standards, including using string literals, eliminates the "ugliness" of the null assignments when unassigning values, removing <any> casting and adding comments to provide clarity.

[codecov-io]

Current coverage is 97.48% (diff: 100%)

Merging #189 into master will increase coverage by <.01%

@@             master       #189   diff @@
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  Files            43         43          
  Lines          2222       2224     +2   
  Methods          26         26          
  Messages          0          0          
  Branches        410        416     +6   
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+ Hits           2166       2168     +2   
  Misses           53         53          
  Partials          3          3          

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[agubler]

👍

[agubler]

Okay can we take the styling offline? I think after that then this is good to go 👍

[tomdye]

merge away 👍