feat: improve regex analysers in XML

[gandarez]

This PR improves the regexes analysers in XML by adding the single attribute and changing how regex nodes are implemented. Some analysers break in the first match where others sum all scores and return, the single attribute when true returns the score for the first match. The regex order matters.

<analyse single="true" >
      <regex pattern="(?m)^\s*#include &lt;" score="0.1" />
      <regex pattern="(?m)^\s*#ifn?def " score="0.1" />
</analyse>

Ref #828

[alecthomas]

Nice, thanks!

[gandarez]

Thanks for merging it. Any plan to release it soon?