Dependencies on plugins

[Rich-Harris]

In an AMD/CommonJS context, this makes sense (to make the custom tap event available to the component):

require('ractive-events-tap');

But ractive-load will look for Ractive.load.modules['ractive-events-tap'], and then window['ractive-events-tap'], and then (having found neither) throw an error.

A workaround is to do Ractive.load.modules['ractive-events-tap'] = Ractive.events.tap, but that sucks.

Options:

1. Disregard any dependencies that match the pattern /^ractive-/. Ractive will print a warning when it tries to use the plugin and finds it missing.
2. Don't throw an error, just carry on. Would make debugging harder in other situations (e.g. if you did THREE = require('three'), you wouldn't realise that for modules with a name/exports mismatch, you need to alias them with Ractive.load.modules.three = THREE;