Feat/rescue missing

Check out Line 13 of lib/effective/liquid_mailer.rb: https://github.com/code-and-effect/effective_email_templates/compare/feat/rescue-missing?expand=1#diff-2fa01276592dcc2c4d3e021beda4af02R11

I want to rescue from a missing template error but I'm not sure what the best solution is.  Rescuing is advantageous because templates are stored in the database and there could be emails trying to go out (perhaps in a User::after_create hook) that prevent actions in a brand new app.  I'm thinking that adding a logged error is the best solution for now but it would be nice to have a customizable response in the long run.