Object plugin

[6utt3rfly]

Adds Object Expression support as a plugin, from issue #39

(builds on #143)

NOTE: doesn't build into the dist folder yet...

[6utt3rfly]

@LeaVerou - I spent awhile playing with the rollup config, given that this is the first plugin. I could use your thoughts on how plugins should be bundled...

if the plugin is added by the end-user with a simple import '{plugin}', then that plugin needs to import jsep. If plugins are built as an extra step to a separate output file, then each plugin will create its own copy of Jsep (and then it wouldn't work for multiple plugins). I was able to add a replace import jsep from '../jsep.js' with just import jsep from 'jsep', and then a custom plugin to prevent including the jsep file in the output, but that makes it more problematic if using a minified, iife, cjs, or other version.

{
  name: 'ignore-import',
  resolveId: source => source.includes(name) ? null : false,
},

If each plugin is a function that takes jsep as an argument, then it would not have any imports and could be bundled as separate file easily. Using a plugin would then be like:

import jsep from 'jsep';
import plugin from '...';

jsep.addPlugin(plugin)
// or:
plugin(jsep);

I looked at our discussion in #123 ... but thought you might have some further thoughts on how to proceed?