feat(power-assert-formatter): use EventEmitter to make renderers customizable
chore(power-assert-formatter): rebuild web bundle
feat(power-assert-formatter): customize rendering by using custom renderer constructor in `renderers` option

if string, just require it. if function, treat it as renderer constructor.
chore(power-assert-formatter): rebuild web bundle
chore(power-assert-formatter): update devDependencies
docs(README): add API documents for defaultOptions function
chore(power-assert-formatter): rebuild web bundle
refactor(power-assert-formatter): simply get/setParent
feat(power-assert-formatter): move built-in renderers to ./built-in/

BREAKING CHANGE: built-in renderers are listed as relative-paths

If you are customizing renderers by `options.renderers`, you may have to migrate.
To migrate, change your code from the following:

```
[
    'file',
    'assertion',
    'diagram',
    'binary-expression'
]
```

To:

```
 [
    './built-in/file',
    './built-in/assertion',
    './built-in/diagram',
    './built-in/binary-expression'
 ]
```
chore(power-assert-formatter): rebuild web bundle
refactor(power-assert-formatter): extract location.js out
refactor(power-assert-formatter): use strict!
chore(power-assert-formatter): rebuild web bundle
Merge pull request #10 from twada/renderers

Customizable Renderers