Describe 0.4.0 improvements for scc unrebased-prs
Document new --check-commit-status option
Add description of new scc check-status command
Fix typo
Fix minor nitpicks
Merge pull request #549 from sbesson/rebased/dev_4_4/scc_040

Document changes in scc 0.4.0 (rebased onto dev_4_4)