Support background and foreground default color headers

[markqvist]

A while back, nomadnet added support for specifying the default background and foreground color of pages as header tags:

Page Foreground and Background Colors

To specify a background color for the entire page, place the `!#!bg=X`! header on one of the first lines
of your page, where `!X`! is the color you want to use, for example `!444`!. If you're also using the cache
control header, the background specifier must come `*after`* the cache control header. Likewise, you
can specify the default text color by using the `!#!fg=X`! header.

I don't think micron-parser supports this yet, but it would be very nice if it did! Should be relatively simple to add, since it just needs to check if the !#bg=XXX or !#fg=XXX are present in the document, and then apply a default color style based on that.

[RFnexus]

There seems to be something odd going on over in NomadNet with interpreting the bg / fg headers. Not sure if this is the intended behavior or not.

NomadNet version 0.9.1, tested with gnome-terminal and alacritty.

[markqvist]

Definitely something wrong there. Will have that fixed shortly.

[RFnexus]

Let me know if this looks good to go over on the JS end of the Micron parser:

[markqvist]

All good, that's looking like it should.

I've also fixed the fg/bg parsing problems in nomadnet in markqvist/NomadNet@dbd1d87.