Document mixes of pkg_* and new-style declarations
Complete the repository descriptions.
Document the usual cases for pkg_*
Move to documentation.
Add more explanation in 2013-04-05-package-management.md

Explain a bit more about when the escaping syntax is required, and why it's important to use the conditional assignment when asking for "any" version of a package.
Merge pull request #2 from ned21/package-management-docs

Add more explanation in 2013-04-05-package-management.md
Merge pull request #29 from piojo/package-management-docs

Document package management in Pan code