Merge pull request #32 from csmith/master

Tell gradle to use 1.8.
Add java 8, run away from Dataforce
Switch to 8 in gradle.
Merge pull request #33 from greboid/java8

Add java 8, run away from Dataforce
Tidy up gradle source sets.

This replaces the default source directories (src/main/java, etc)
with our own, instead of just appending ours to the list.