Implement separate file compilation in Sparrow

[lucteo]

For larger projects, we may have multiple sparrow source files that we would like to compile individually.

Main ideas:

• non-generic functions are only compiled (e.g., code generation) for the translation unit in which they appear
• each function (and class) should have an unique name, so that we can properly find the symbols at link time
• the same generic can be generated into multiple files, but at link time, they should all collapse to only one

Make sure this works at least with the Sparrow parser code.