Don't run post build during PR testing

Check Travis's env variable TRAVIS_PULL_REQUEST to see if the post build
should be run at all
Use public Travis build number in commit message

I previously set the job ID instead of the build number as described in
the documents
http://about.travis-ci.org/docs/user/ci-environment/#Environment-variables
Use extends rather than regular expressions

More selectors, but better performance
Use @each expansion for downloadable file types

Adds readablity and maintainablity
Space not required after mailto:
background-position: 0 0 is the default value

This is not the case with multiple backgrounds, but that does not apply
to icons
Extend download iterator

Previous version output single classes for each member of the array
Use iterators for sprites

Note to change the sprites to a single column at a later date
Use sequential gem install

For issue with Travis
Merge pull request #946 from nschonni/sequential-gem-install-940

Use sequential gem install
Merge branch 'travis-skip-pull-requests' of github.com:nschonni/wet-boew into v3.0
Confused font sizing rule

Rule seemed to be used to use the common font, as font sizes where
specified for all the elements elsewhere
Merge branch 'refactor-icons' of github.com:nschonni/wet-boew into v3.0
Merge branch 'duplicate-font-size-base-scss' of github.com:nschonni/wet-boew into v3.0
Merge pull request #947 from LaurentGoderre/v3.0

Merge PR #943, #928 and #944
Merge branch 'v3.0'