Add a miniscule password retriever

This primarily exists so the user gets a helpful prompt when Security
Services asks them to grant keychain access.
spike at adding write support to our keychain helper
spike at integration keychain helper
C, I barely speak it. Also, this is horribly inefficient, but who cares?
cleanup
store the oauth token in the Keychain as well
KEYCHAIN_SERVICE -> KEYCHAIN_PASSWORD_SERVICE
we control the stderr, let's ignore it
Print error codes from Keychain API to stderr
Be more specific about KEYCHAIN_PASSWORD_SERVICE
Extract keychain fun
Be consistent about naming
No need for OSStatus here
Merge branch 'master' of https://github.com/boxen/boxen into keychain-helper
Merge branch 'keychain-helper' of https://github.com/boxen/boxen into keychain-helper
Pull in feedback from Slava
preface error messages with Boxen Keychain Helper
fix
shellescape keychain gets and sets
spike test