rename bundle to archive throughout (mechanical change)
rename bundle to charm; rename receiver variables
rename Archive to CharmArchive etc
gofmt
rename Read to ReadCharm
Merge remote-tracking branch 'origin/master' into bundledata

Conflicts:
	charmdir.go
rename import paths
Merge branch 'rename-bundle-to-archive' of github.com:rogpeppe/charm into rename-bundle-to-archive
Merge pull request #8 from rogpeppe/rename-bundle-to-archive

charm: prepare for adding bundle support