Add support for HTML namespaces, such as SVG

[MaddyGuthridge]

Currently, PyHTML only supports the main HTML namespace. It would be awesome to add support for other namespaces such as SVG to be able to group tags.

Potential usage:

import pyhtml as p
from pyhtml import svg  # serves as the svg tag in the main namespace as well as an entry-point to the SVG namespace

p.html(
    p.body(
        p.svg(  # same as just svg
            svg.path(...),
        ),
    ),
)