BF: removed unused export from test __init__

Failing relative import; not needed in any case.
RF: move atoms tests into atoms directory

Move atoms tests into atoms code directory.
RF: move .gitignore contents from code directory

.gitignore got left behind when moving files out of the code directory.
BF: change location of code directory for reorg

We moved the code directory; point the docs at the new directory.
NF: add .gitignore for generated api doc path

source/api directory generated by doc build; ignore in git.
RF: remove another couple of stray setups

setup.py files I missed in the original refactor to avoid using numpy
distutils.
Merge pull request #4 from matthew-brett/post-move-cleanups

MRG: some cleanups after code directory move.