Reworked next() and prior() taking the distance arguments.

The new version should provide the expected behavior in the case (prior(v.end(), v.size()) == v.begin()). It should also work with integers now, as was originally intended by David Abrahams. Added tests to verify these new use cases.
Merge pull request #15 from boostorg/next_prior_fix_iterator_backtracking

Reworked next() and prior() taking the distance arguments.
Add a redirect for the compressed pair docs.
Merge pull request #16 from danieljames/compressed-pair-redirect

Add a redirect for the compressed pair docs.
Add metadata file.
Merge pull request #18 from danieljames/metadata

Create metadata file.
Moved enable_if to Boost.Core.
Merge branch 'develop'