resolves #43 support text formatting in footnote content

[mojavelinux]

• match inline patterns inside footnote content
• change name of match to markup.other.footnote.asciidoc
• skip escaped footnote
• add CSS for footnote (map to function color)

[nicorikken]

I tried this one, works nicely.

[nicorikken]

@ldez Do you agree with still merging this in its current state, leaving open that the styles need refactoring in naming/styling?

[ldez]

I agree. Merge is ok.