Search all faces in file

[asinghvi17]

Currently, it looks like FreeTypeAbstraction only searches the first face in each file, as can be seen here.

https://github.com/JuliaGraphics/FreeTypeAbstraction.jl/blob/b7d6d65832e46047225bc02579ba7d124b38ebe2/src/findfonts.jl#L143

try_load only loads the face at index 0 - we should load all faces, and loop through them internally.

We can get the number of faces in a file by this operation.