Make sure Frontmatter data is actually cached. Fixes #903

(Can't return a value to early out of a begin…end expression in Ruby)
Cache frontmatter repeated calling of recursively_enhance
loosen thor dep now that we're bundling padrino
Merge pull request #906 from adamesque/master

Make sure Frontmatter data is actually cached
Ruby 1.8 can't regex on a symbol (or something)
jruby isn't optional
stub out blank middleman-more gem for backwards compat with extensions
move vendored gems into shared root
unneeded require
ignore tmp dir
Listen bundles these gems again (le sigh)
after_build support in class-based extension
Make Frontmatter a class-based extension to simplify file
Cache the filtered resource list to avoid calling Resource#ignored? a ton