display of SSL endpoint info, ability to add certs

Added ssl and ssl-cert-add commands.
add ssl-cert-rollback command
cleanup addon-destroy warning
add ssl-destroy command to remove an SSL endpoint
zsh completion for ssl commands

Fixes #143.
complete all files, not just .pem (thanks @dpiddy)
handle the nonexistent netrc case inside hkclient
use fatal errors in auth where appropriate
Only read body for PATCH/PUT/POST.
Add addon-plan command

Enable users to change (upgrade/downgrade) an addon's plan.
basic completion for addon-plan
update speakeasy to resolve #147
Rename printUsage() -> PrintUsage()

Also rename printUsageTo() -> PrintUsageTo()
print short usage on usage errors
improve error msg on scale w/ duplicate dyno type

Fixes #133.
Example -> Examples