[WIP] Refactor classes -> factory functions

[nfantone]

• Avoid using class or new.
• Reduce usage of this.
• Favor composition and factory functions.
• Expand documentation all around.
• No API changes.

TODO

This is not to be merged until all of below are done and dusted:

• Improve jsdocs.
• Adapt and fix unit tests (make CI test pass).
• Add functional, end to end tests using rabbitmq on Travis.

[codecov-io]

Current coverage is 100% (diff: 100%)

Merging #73 into develop will not change coverage

@@           develop   #73   diff @@
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  Files            4    10     +6   
  Lines          120   197    +77   
  Methods         22    38    +16   
  Messages         0     0          
  Branches        13    26    +13   
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+ Hits           120   197    +77   
  Misses           0     0          
  Partials         0     0          

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