Fix .gitmodules.  Switch external/cgmath-rs to my own fork.
Pull external/cgmath-rs.
Pull changes again from external/cgmath-rs.
Switch external/rust-png back to master since fixes were merged.
Pull external/rust-png.
Fix the broken Makefile and Android.mk.

Still need to fix so that manual steps copying libpng.a and libshim.a
happen automatically.
Renderer saved state contains a set of blocks to render.