Regex comparison issue when using Latex notation

[GluonicPenguin]

If marking signal contributions using Latex e.g. including backslashes, cannot generate this in the plot given this regex comparison line (https://github.com/FAST-HEP/fast-plotter/blob/master/fast_plotter/utils.py#L77) will raise an error re.error: bad escape \X at position Y.

Workaround is to manually append latex-formatted string to the first_values array, with double-backslashes. This is due to the known re.match issue when including "" in string.