Add possibility to run selected code from a temporary file instead of passing code in args

*context.getFileWithCode()* can be used in grammars instead of
*context.getCode()* allowing to run selected code with languages that
don't have interpreters like "php -r". Tested with PHP on Win7 (see example in
grammars.coffee with PHP language)
On windows it's very usefull because I had some problems with linebreaks in terminal causing some parse errors...

EDIT: Added dependency to node-uuid used in filepath
Prefer unless over `if !`, i.e. `unless fs.existsSync(@tempFilesDir)`.