Some slight modifications to get Prism highlighting to work

Some slight modifications to get Prism highlighting to work. 
- Quick change was lowercasing the language name. ```language-C``` to ```language-c```
- The little more involved modification required dynamically adjusting for ```language-C++``` to ```language-csharp```
- Added [Powershell](https://github.com/pezhore/prism-powershell) support