add the `_loadModule` internal helper and use it to refactor _ThemeProxy and _ModeProxy ctors
examples : the `<meta charset="utf-8">` in the `<head>` mitigates the need for setting `charset` on the script tags
add the `_ace` and `_stringify` internal helper functions and use them to refactor
rename the first argument of `_loadModule` to `moduleType` to match the javascript
Mode : expose a getter for the `path`

Add coverage in the mode tests for expected path when using the `new
Mode.forFile` ctor
add tests; fix some code; merge to master