Altered Project Structure / Updated Ionic.Zlib.dll / Added required source files to compilation / Updated .gitignore 

I have updated the renamed external to libs because this makes it more clear these are external libraries. I have also added an AssemblyInfo.cs though have not populated. The missing AssemblyInfo.cs was the first reason I was not able to build this using Mono Develop. I have moved the source files to a src directory rather than leaving them top level. I have also now excluded the bin directory from the repo because these files can be generated locally. Any files that cannot be generate locally and are used as tools should be added to a directory called tools. I have also updated the Ionic.Zlib dll to the latest version to allow it to be compiled with more up to date version of .NET / Mono.

**Note :** You may need to fix the reference paths when building.