Fixes for Heroku dev clouds.

Read creds from proper netrc entry and disable SSL verification if
HEROKU_API_URL is set.

Fixes #80.
suggest help topics as help commands

fixes #78
add tests for dev environment usage
sshkey-add -> key-add
add keys and key-remove commands
log-drains -> drains
use printError()
update Godeps for go-netrc and heroku-go
tweak unix section in readme
escape ampersand in openURL on windows
don't error out when no creds are found
add login command
logout command and styleguide update.
fix panic when machine doesn't exist in netrc
print login message on unauthorized errors
2FA login support
fixup Postgres dev usage. Use addon config_vars

The addons API now returns a list of config vars that addon is
responsible for. Use that data to map Addons to env vars rather than
solely using string manipulation.

Also fix Heroku Postgresql dev usage to match how it works in the
toolbelt.
fix tests for postgresql client URL overriding
add regions command to list available regions
cleanup sloppiness in regions command