charm: add BundleArchive
Merge branch '006-bundlearchive-2' into new-branch

Conflicts:
	charmarchive.go
change README to README.md
Merge pull request #15 from rogpeppe/006-bundlearchive-2

charm: add BundleArchive
add tags to bundledata
Merge pull request #17 from jrwren/v2

add tags to bundledata
add description to bundledata

add field to match Bundles Specification propsal
fix typos
fix typos
Merge pull request #19 from jrwren/v2

add description to bundledata and pick docs from master