handle issues with generated function names

[minhnh]

As discussed in #15 (specifically in #15 (review) and #15 (comment)), the following issues with generated function names should be better handled:

• check names of generated functions to ensure that they are unique
• ensure name used for function declaration, definition and function call are all the same

One way to deal with the 1st point is to utilise the built-in "unique name" generation to enforce uniqueness. I have tried this out a bit, however, and it seems to be non-trivial to ensure the 2nd point with this method. Specifically, I tried to create a function name template to provide an unique function name that are used in function declaration, definition, call templates. The generated strings are unfortunately all different for the different templates.

@scymtym @xwavex @svenschneider please add anything you notice