Wrap Milestone in an object to display extended information

Use Milestone.__str__ in scc milestone list
Add milestone delete command and use command logger
Move get_milestones() and get_milestone() to GitHubRepository class
Fix description setting in `scc milestone create`
Add close subcommand to scc milestone
Set no_wait to True in get_rev_list()
merge master -D org: PR 157 (Milestone command)
merge master -D org: PR 158 (Fix scc check-prs by using find_branching_point())
merge master -D org

Repository: openmicroscopy/snoopycrimecop
Already up-to-date.

Merged PRs:
  # PR 157 sbesson 'Milestone command'
  # PR 158 sbesson 'Fix scc check-prs by using find_branching_point()'

Generated by SCC-merge#291 (http://ci.openmicroscopy.org/job/SCC-merge/291/)