Revamp build process to separate locale data

This changes the build process of this package to separate the locale data from the runtime lib.

When using this package in Node.js, the library will still be primed with all its locale data. _But_ on the client, it won't. The `dist/` dir now has the following structure:

```
dist/
├── intl-messageformat-with-locales.js
├── intl-messageformat-with-locales.min.js
├── intl-messageformat.js
├── intl-messageformat.js.map
├── intl-messageformat.min.js
└── locale-data
    ...
    ├── en.js
    ...
    ├── fr.js
    ...
    └── yo.js

1 directory, 157 files
```
We used to have `src/full.js` checked in. This replaces that, defaulting the library to English. @caridy asked that I check it in so people could look at the `src/` dir and see everything is there.