Update documentation to reflect (anticipated) v0.5.0
Add page about usage of SBT plugin

Also fixes #37: Document how to cross build
Improve documentation structure
Add links to CLI distribution
Add links to API docs
Fix #25: Add tutorial to quick start new devs
Add big "latest release" button on front page
Merge pull request #38 from gzm0/update-0.5-changes

Update documentation to reflect (anticipated) v0.5.0