Add test for graphite-project/graphite-web#658
New pep8, new restrictions
Reformat release notes and list graphite-web issues
Make sure the new step is an int
Unpack lists for more robustness
Make sure HH:MM values are allowed
Make sure constantLine has a pathExpression
Add a test for sumSeries

Refs graphite-project/graphite-web#588 which seems already fixed.