Merge pull request #893 from bhollis/master

Some small improvements
update some deps
High-level 3.1 changes
bump
add CONTRIBUTING.md / LICENSE.md, rejig README.md / .gemspec
Merge pull request #897 from middleman/readme-license-contributing

Readme / License / Contributing
fix test for updated uglifier
Merge branch 'master' of github.com:middleman/middleman
reorg some of the more stuff
vendor padrino
The file watcher knows which files exist, so don't use slow File.exists?

Possible solution for #903
Fix c9d151ba667aa84ec08c14508a01f0071826eccb for when files are outside the project
Cache the filtered resource list to avoid calling Resource#ignored? a ton