Added some c snippets and snippet switching.

After a crash course in keeping git feature branches sync'd with a remote, lets try this again!

From #172 
> When trying to write snippets I've found the desire to quickly switch between the python and the generated snippet file. This is a little `fswitch` rule that I've used locally for a while and thought it could help others. I also added a few C snippets that I felt were missing.

> For the `fswitch` rule I expanded `SetFswitchVars` to allow an optional argument for `b:fswitchfnames`. There may be a better way to do this but it's what I figured out with my limited exposure to vimscript!

Let me know what you think!