Add BranchVersion
Support BranchVersion in Version.create
Refine VersionConstraint specs a bit
Add missing specs on VersionConstraint.parse
Ignore trailing spaces in a version constraint
Support BranchVersion in VersionConstraint
Refine a spec on LockFile#flavors
Refactor LockFileParser on plain_version
Support BranchVersion in LockFile/LockFileParser
Simplify FlavorFile#flavor with keyword arguments
Refine test descriptions on FlavorFile
Support FlavorFile#flavor with a branch option
Add a NEWS section
Update the Philosophy on BranchVersion
Add the introduction on Branches
Add scenarios about installing with branches
Add scenarios about upgrading with branches
Add scenarios about changing tracking branches
Add scenarios about detecting incompatible branch
Define "$repo has $branch" step