superscript and subscript characters should extend past cap/base lines

[Adam Dingle]

I'm using ubuntu-font-family version 0.80 in Ubuntu Quantal.

In the Ubuntu fonts, superscript glyphs (such as the 2 in x²) and subscript glyphs (such as the 2 in x₂) should appear higher and lower than they do today. Currently these glyphs stop at the cap line (above) and the baseline (below). The Wikipedia article on Unicode subscripts and superscripts (http://en.wikipedia.org/wiki/Unicode_subscripts_and_superscripts) has a nice explanation of why this is incorrect:

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  Most fonts that include these characters design them for mathematical numerator and denominator glyphs, which are smaller than normal characters but are aligned with the cap line and the baseline, respectively. When used with the solidus, these glyphs are useful for making arbitrary diagonal fractions (similar to the ½ glyph).

  This was not the intended use of these characters when Unicode was designed. The intended use was to allow chemical and algebra formulas to be written without markup. Proper appearance of these requires true superscript and subscript [glyphs].
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This is related to bug #683186.