More renames
More renames

- Renamed `stbtt__GetCodepointBitmapBox` to `get_codepoint_bitmap_box`
- Renamed `stbtt__GetCodepointBitmapBoxSubpixel` to
`get_codepoint_bitmap_box_subpixel`
- Renamed `stbtt__GetGlyphBitmapBox` to `get_glyph_bitmap_box`
- Renamed `stbtt__GetGlyphBitmapBoxSubpixel` to
`get_glyph_bitmap_box_subpixel`
- Renamed `stbtt_FreeShape` to `free_shape`

PistonDevelopers/truetype,PeterReid/truetype