Fix referencing problems and tidy up directory structure

Hi Dave, it's been a while!

Here a few _suggestive_ commits for how I would handle references (including the tricky beast that is Plankton).

This includes shuffling a few things around, namely the creation of _src/_, _lib/_ and _bin/_ directories in the repository's root. Source code goes in the _src/_ directory and I've updated the _csproj_ file to reference libraries from the _lib/_ folder and also to build the project into the _bin/_ directory.

Of course, these are all suggestions -- do with them what you wish!

A screenshot below of everything working (even with_ COFF loading_ enabled):

![image](https://cloud.githubusercontent.com/assets/121068/2878650/d8bd837c-d45f-11e3-98f1-a8b2a59bbbf0.png)

Incidentally, I believe the _COFF loading_ error was caused by the project loading **both** PlanktonGh.dll **and** Plankton.gha.