Provide tests for keeping shebang lines in compiled CS files

Shebang lines are currently ignored when CoffeeScript files are compiled to JavaScript. This makes it quite hard ( although not impossible ) to create executable scripts on Unix-based systems.

The resulting JavaScript file should preserve the shebang line from original CoffeeScript file if present and if it is on the first line of the document.

Since I am not that skilled to implement this functionality in the compiler myself I am at least sending the tests describing the expected functionality.

PS. This has been already discussed in #2216 although a conclusion has not been reached there.
Thank you!