Add a few more test cases; general test file cleanup.

Note: Major change is moving everything into a try/finally
so the filter mmap files aren't left lying around when the suite fails.
This makes local testing a bit nicer because one doesn't have to
rm -rf /tmp/*.mmap between test failures.
Update bloom-filter.jl

added in()
Update bloom-tests.jl

Added a quick test for in().
rebase and use Base.in
README
Merge pull request #9 from sbromberger/function-in

RFC: add in()