Keep styles that can't be inlined in a style tag.

[lambacck]

Some styles can't be inlined (for instance media queries and pseudo
elements). This change adds those styles to a single stylesheet which
gets inserted inline just below the open body tag. This is known to at
least work with the Ink email css framework by Zurb.

[lambacck]

I just added another commit that fixes a bug where the specificity of the selector overriding an existing style is not recorded.

[dlanger]

@lambacck Sorry for not merging this earlier - for some reason GitHub wasn't sending me emails that things were happening here. I'll do some work this weekend to get this in.

[pySilver]

any updates?

[slara]

This is necessary for media queries and no other alternative has it. Adding this would be really great.

[dlanger]

@lambacck I'm a bad person and let this languish for a long time. I've switched to requests (as you did here), pep8'ed the source, and started to add some tests...which should make it easier for me to accept PRs.

If you're still interested, it'd be great if you updated your PR to be mergable, and we could finally get this if. If not, I'll try to do it myself over the coming while.