combine into single stage
rename function name
simplify symbolic differentiation
imports
merging two stages
register kryo registrator
spark 1.1 in gradle
update spark download link
Merge pull request #9 from pkoperek/opt/simplification

Opt/simplification
Merge pull request #10 from pkoperek/opt/kryo

Opt/kryo
use snappy-java 1.1
Merge pull request #11 from pkoperek/opt/spark_1.1

Opt/spark 1.1
cache parsed input file
fixed unit test + a bit of refactoring
Merge pull request #12 from pkoperek/opt/cache-input-file

Opt/cache input file
jvm tuning options