Improved Cljs compilation times by 4-5x
Improved Cljs compilation times by 4-5x

Based on http://swannodette.github.io/2014/12/22/waitin/

- added "target/classes" to :source-paths
- added :clean-targets to remove only project specific out
- updated cljs to 0.0-2511
- added :cache-analysis true to compiler settings

On my MBP (2013 2.3ghz quadcore i7), a cold compilation takes ~6s. Subsequent compilations ~2.1s.

With these settingsm, subsequent `lein clean` and `lein cljsbuild once` compilations take
~0.35s.

DjebbZ/mies,fdserr/mies,fdserr/mies,DjebbZ/mies,bensu/mies,whamtet/cljs-server-template,pandeiro/jamal,niwinz/mies,swannodette/mies,swannodette/mies,bensu/mies,niwinz/mies