Merge pull request #477 from oxtopus/fix-travis-builds

Derive $NUPIC from $PWD and $TRAVIS_REPO_SLUG
Update DOCS.md
Documenting Segment.dutyCycle

Also using as an example of documentation for the wiki page.
Merge pull request #481 from rhyolight/docs

Documenting Segment.dutyCycle
Applied a different Doxygen style.
Merge pull request #482 from rhyolight/docs

Applied a different Doxygen style.
Triggering fresh Travis-CI build.
"The fix for this has been rolled out, let us know if you're still seeing any issues!" </snip>

Revert "Derive $NUPIC from $PWD and $TRAVIS_REPO_SLUG as https://github.com/travis-ci/travis-build/pull/182 may not be deployed yet"

This reverts commit 65ba48645eb29f64062679646a8b8335c4af1026.