latin-ext: Add U+218A and U+218B to latin-ext + GF Latin Expert Set

Unicode 8.0, released in June 2015, includes `U+218A` (`turned digit two`) and `U+218B` (`turned digit three`). It would be nice if each font featured its own designs for these characters, but it will not be the common case.

Fortunately the simplest and most obvious forms for these characters to take in any given font are 180° rotations of `2` and `3`, which are always present. Would it therefore be reasonable to run a script over all the fonts, checking for the presence of the new characters, and filling in transformations of each font's `2` and `3` where appropriate? I am currently doing this on my own for each font I use with a need for these characters, but since the solution lends itself to automation, why not enhance this whole set upstream, at least where licensing allows?