Add find() variants.

[tzlaine]

No description provided.

[tzlaine]

Lemme know if you want me to drop the .travis.yml bit. If you like the idea of CI for Boost.Algorithm, I'll add an Appveyor script for MSVC support.

[mclow]

BidiIter find_backward(BidiIter first, BidiIter last, T const & x)
East const, Zach?

I think I'd rather you proposed the CI stuff as a separate commit. That will keep the change log cleaner. I don't have a problem with the CI stuff, I'd just rather it was separated.

[tzlaine]

There, how's that? I'll prepare an Appveyor script too before submitting the CI piece.

[mclow]

Thanks. Please watch the test bots; and ping me in a week or so to merge to master.