Merge pull request #20 from laurisvan/master

Add SASS sourcemaps into the build; fix JSCS errors in gulpfile; Test dev & production modes in Travis.
Simplify installation instructions

- global gulp is not needed
- combine gem install commands
Merge pull request #22 from apaatsio/update-installation-instructions

Simplify installation instructions
Move SASS styles into 'styles' directry (better semantics)