Generate unique names that do not collide at the C level

[EliasC]

Fixes #69, fixes #94. This commit unifies the generation of C-level
names and adds a unique prefix to all generated names. Makes the
generated code more ugly unfortunately, but on the other hand you can
name your variables "default".

[kikofernandez]

@EliasC could you add a test file for this PR?

[EliasC]

@kikofernandez Will do!

[kikofernandez]

@EliasC there are some conflicts and it cannot be merged. could you fix the conflicts and rebase? Let me know as soon as you rebase. The PR should be ready to go!

[EliasC]

It seems there are seven commits that do not belong in this PR added by @kikofernandez. Do you know what's going on?

[EliasC]

@kikofernandez I think I fixed it, but could you still check if you accidentally committed some task stuff to my fork? The tests that are failing are async_force_gc, async_foreach and largestream, all without any compiler output which would be the case if there was name problems (and I thought they were all disabled in Jenkins?).

[kikofernandez]

not sure what's going on with those 7 commits... can't see them in the history... I guess you rebased and removed them? My comment was more related to not being able to merge the PR. Tests pass!