csclient: make Do more general; make Get do more work
Merge pull request #151 from rogpeppe/065-csclient-more-general-do

csclient: make Do more general; make Get do more work

This will make it easier to implement archive downloading without
duplicating code.
internal/charmstore: return blob hash when downloading a charm archive
Merge pull request #152 from rogpeppe/067-archive-download-return-hash

internal/charmstore: return blob hash when downloading a charm archive

We want clients to get the hash as well as the data.
remove legacy API info from README

Move the API docs into the legacy package.
Merge pull request #153 from rogpeppe/068-remove-legacy-README

remote legacy API info from README

It's misleading and unnecessary.