Added formal branch policy.
Clarified PR vs. issue + expected branch deletion.
Add optionalDependencies badge to README.md

Fixed by alanshaw/david-www#123
Merge pull request #176 from sun/policy-branch

Formalize the public feature/topic branch policy
Merge pull request #193 from markcarver/optional_dependencies

Add optionalDependencies badge to README.md
Merge branch '1.x' into sun