[Update] Add gulp-gzip and gulp-watch

(browserify.js):
Add gzip condition on production flag

(stylus.js):
Add gzip condition on production flag
Watch now occurs within the (stylus.js) module. Switched default watch
with more robust module.

(gulpfile.js):
Removed redundant stylus watch code. Added HTML watch for Jekyll output.
HTML files are gzipped and renamed on production flag.