This change removes wrappers inherited from Gfx::Typeface for WOFF and
WOFF2 fonts. The only purpose they served is owning of ttf ByteBuffer
produced by decoding a WOFF/WOFF2 font. Now new FontData class is
responsible for holding ByteBuffer when a font is constructed from
non-externally owned memory.
An error is now returned if `numTables` is zero or greater than 4096.
While this isn't explicitly mentioned in the specification, subsequent
calculations will be incorrect if the value falls outside this range.