Add support for class param declarations at the constructor

[shannon]

My main motivation for this was that VSCode intellisense does not work when constructor params are defined at the class declaration, it expects them at the constructor.

So I just merged the params from a constructor comment during the infer phase.

Relevant issue: #689

This was my first look into this code and I couldn't get the build to work locally let alone the tests so I'm hoping the tests can be checked in circle.

Edit: Just to clarify, I did actually test that it did what I wanted to by editing my local node_module/documentation/lib files directly. I was getting flow type syntax errors on build and I'm not very familiar with flow so this was the easiest way for me to work with it.

[coveralls]

Coverage decreased (-0.04%) to 86.068% when pulling 64185e8 on shannon:master into 647fdf4 on documentationjs:master.

[tmcw]

Thanks