interp_api_cleanup branch

[Andrew Whitworth]

The interp_api_cleanup branch was contributed by a GCI student in
response to a task I created. The branch merges the files
src/interp/inter_misc.c and src/interp/inter_create.c into a new file
src/interp/api.c. It also renames all public functions in that new
file to have the standard "Parrot_interp_*" prefix.

Parrot, NQP, and Rakudo all build and pass tests for me on my machine
(I have only run Rakudo "make test", not "make spectest" yet. I don't
expect different results).

Some extra testing and review would be appreciated. If there are no
complaints I will try to merge this branch as early as tomorrow.

Thanks.

--Andrew Whitworth