Update csharp-mode package to maintained copy on Github

**NOTE:** This request is replacing a un-maintained csharp-mode package with a fork.

**Reason for forking:** Package has been un-maintained since 2011 and contains several
bugs, which among other things breaks tooltips (for all modes) and in emacs 24.4 it doesn't even run. I would consider this "extreme" enough to warrant forking.

Original author has been contacted via several means, but no reply has been received.

**Original, un-maintained sources**

Un-maintained version found on EmacsWiki dated 2013. Does not include all fixes as found in Google Code per May 2011.

http://www.emacswiki.org/emacs/csharp-mode.el

This version was originally based on the following version found on Google code, which has been 100% un-maintained since 2011, with several abandoned issues:

https://code.google.com/p/csharpmode/

This pull addresses csharp-mode issue https://github.com/josteink/csharp-mode/issues/6