Issue #374: hyphenated class names

Hi Rene! This branch fixes issue #374 by modifying the jsonp generator to write `Ext.data.JsonP["callback_name"]` instead of `Ext.data.JsonP.callback_name` and by separating class and member names in URLs using a tilde instead of a hyphen.

One thing that we might be able to improve here is that the `~` is hardcoded in a few separate places, as the `-` was before. It would be nice if we only had to define it in one spot (in the Ruby, at least) — but there isn't a particular one that would obviously be the right location to do that.

For a simple demonstration of the fix, check out the `test-issue374` branch in my fork (i.e. scottrobertwhittaker@51061901e7dfca343e9763f97d2e5bed176c6ced) and run 

    jsduck --builtin-classes --guides=guides.json --output=docs

Looking forward to hearing what you think!