Support input pipes

http://sourceforge.net/p/xetex/feature-requests/12/
Fix a thinko

Mixed direction case was broken in 9fc8269, glyphs and position arrays
star from 0 for each run, unlike glyphIDs and locations.
Simplify

Trust HarfBuzz and allocate as much glyphs as it says.
Minor WEB code formating
Better XeTeX logo in WEB
Don't duplicate table definitions and use sfnt.h
Fix XeTeXFontInst::unitsToPoints()

It should return float not int!
Remove unused getKernPair
Use Offset type for human readability
Typo
Initial support for reading OT math kern
Implement math kerning at TeX end
Make error messages a bit more useful
Guard against mixing native and tfm fonts
Minor
Support Graphite line breaking with HarfBuzz

Needs Harbuzz patch for Graphite font/face getters...
Import Graphite2 and new HarfBuzz from TeX Live
Update to the API from HarfBuzz master
Pass features to Graphite2 break iterator
Pass the string script and language tags around

So that we don’t have to reverse engineer them from
hb_(script|language)_t when passed to Graphite2.