Easier text decoration

[hchauvet]

Add a way to highlight part of text using simple syntax inside the text command.

Example

my_highligth = (
{"color": "Crimson",  "font-weight": "bold"},
{"underline":  ("1px", "lightblue")}
)
text("This is my <equation> $$x = \sqrt{<3 + 5>}{2}$$", highlight=my_highlight)

This will produce "equation" with crimson color + bold weight, and underline "3+5" in latex equation.

We could be inspired by some libraries developed for matploltlib text:

• https://github.com/znstrider/highlight_text
• https://github.com/tomicapretto/flexitext

Works need to be done to decipher if the decoration should be done in Latex before the conversion to SVG by dvisvgm or directly in SVG after the conversion from latex (but in this case we need to link each letter of the python string to the SVG output)