Add a console rake task for convenience
Specify that required ruby version is ~> 2.0, for keyword arguments
Support specifying project name in Econfig.use_keychain (closes #3)
Only initialize the store after #init (closes #2)

This fixes the issue with using econfig-keychain in a Rails initializer,
if you also use econfig for configuring e.g. config/environments/development
Improve the README instructions (closes #1)