Pyramid-assetgen

Added a strict mode (enabled by default) to the ``AssetGenManifest`` so that
if the manifest file doesn't exist, it will throw an error at configure time,
rather than when the first request happens to come in.

Minor tweak to the docs.

Completely changed the api. Instead of using:

request.assetgen_url(name, relative_path)

The integration is now much tighter with Pyramid, using the built in:

request.static_url(path_or_asset_specification, **kw)

And a simpler configuration directive:

use this: no name
config.add_static_view('static', 'mypkg:static')
config.add_assetgen_manifest('mypkg:static')

not this: with name
config.add_static_view('static', 'mypkg:static')
config.add_assetgen_manifest(name, 'mypkg:static')

To achieve this, the `AssetGenRequestMixin` now needs to be inherited as the
**first** superclass to your custom request factory, i.e.:

use this
class MyRequest(AssetGenRequestMixin, Request): pass

not this
class MyRequest(Request, AssetGenRequestMixin): pass

Initial version.