* Fix broken Bulgarian localized of Cyrillic Small Sha and Cyrillic Capital El (#716).
 * Fix broken serif shapes in Italic Cyrillic Small I (#717).
 * Make variant selectors for `m` and `u` have more effect on Cyrillic letters.
 * Fix incorrect serifs of Greek Small Rho (#718).
 * Add derived bold / italic / sans-serif / typewriter letters in Mathematical Alphanumeric Symbols block.
 * Add shorter-serif variant for capital I (#709).
 * Support slope-dependent digit form control (#724).