Fix constant handling and empty else in if compilation
Skip unnecessary block+jump for empty else
Allow jump to use case fallthrough when the jump target is the next block
Make unconditional jump codegen lazy
Reorder blocks to allow more case fallthroughs
update contributing.md about unit-tests
a link to the unit test docs. and a TL;DR section
Merge pull request #298 from albertjan/contributing-md-updates

update contributing.md about unit-tests
update grammar and adsl and generate parser and generate new ast model
skulpt.py to 2.7
updates ast.js to 2.7.6
All tests pass. 1st dictionary comprehension!!
adds set comprehensions

output is different because the set doesn’t get all shook up in skulpt.
Make google closure compiler happy
Adds set literals
Adds debugger statement.
Dry up compgens
Call with null to make goog happy
Rebase on master
Fix last failing tests and make closure happy.