Add @font-face

[dzuk-mutant]

Before I release this package, I want to include @font-face since it's pretty important for a lot of web development.

[dzuk-mutant]

Notes to self: The current problem with doing this is that the internal structure of the package makes it so that it can only accept Property types, while normal properties in Css which return a Style type, even though the supported Descriptors are many normal Css properties (eg. font-weight, font-style, etc.)