Array: Move stride_offset_checked into the Dimension trait
Array: add methods .uchk_at() and .uchk_at_mut()
Array: use uchk_at to reduce .mat_mul runtime by 15%
Array: Move uchk_at_mut method -- it doesn't require Clone.
Update .travis.yml
Update for `use` syntax change.
Merge branch 'master' into gh-pages
Update docs