Use browserify with make

This PR switches to browserify for building the client. It creates two standalone files `dist/share.js` and `dist/share.min.js` which can be loaded in the browser and expose `window.sharejs`.

Also the prototype is updated to directly server browserified versions of the client code.

### Size changes:

**Before**:  41269 (share.js) + 4094 (text.js)  = 45363
**After**: 48281 (share.min.js includes text.js)

I'm not entirely sure why this is bigger, when in #267 it seemed that the size was getting smaler. I will look into this tomorrow.

Ref: #267 

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**Edit** Add size changes info.