Make the hhea ascent/descent match the typo metrics.

[fred-wang]

This makes hhea ascent/descent match the typo metrics to fix rendering bugs in browsers.

Feel free to ignore that pull request if the hhea ascent/descent were intentionally chosen larger.

[khaledhosny]

The existing values were inherited from STIX fonts, I did not want to change them originally to stay compatible with STIX, but I don’t think fixing them makes more sense.

[fred-wang]

However note that in the latest version of STIX fonts the hhea ascent/descent are different (they match the win metrics while those in XITS were smaller). So perhaps the values have changed since you forked.

[fred-wang]

I'm trying to regenerate Web fonts with this change but gets

"downloadable font: table 'cmap': failed to parse table (font-family: "XITS Math" style:normal weight:normal stretch:normal src index:0)
source: http://localhost/ulule/math-documents/xhtml/crystal-structure-20131216/EPUB/css/xits-math.woff style.css
downloadable font: rejected by sanitizer (font-family: "XITS Math" style:normal weight:normal stretch:normal src index:0)
source: http://localhost/ulule/math-documents/xhtml/crystal-structure-20131216/EPUB/css/xits-math.woff"

any idea why?

[khaledhosny]

Can’t tell without access to the files, but seems like a bug with whatever software used to create the WOFF files. No problem with WOFF files I recently added to the repository (at least ot-sanitise from khaledhosny/ots reports no issues).