Merge pull request #14 from rogpeppe/003-router

internal/router: new package

This will be the basis for the new HTTP handling in the
charm store.
Merge pull request #15 from rogpeppe/004-restructure-1

move all top level files to old directory
Merge pull request #16 from rogpeppe/004-restructure-2

internal/...: create new structure for api
Move old -> _old and cmd -> _old.
Merge pull request #17 from bac/rename-old

Move old -> _old and cmd -> _old.