gfx: 1bpp<->2bpp conversion

this is the simplest way to support 1bpp without rewriting a lot
refactor png-to-2bpp conversion
gfx: rewrite lots
gfx: 1bpp-to-png

also dont assume any dimension matches in png conversion
gfx: rewrite lz commands and comments
gfx: direct png-to-1bpp
gfx: make sure rectangular images are also divisible into 8x8 tiles
Merge branch 'master' of github.com:kanzure/pokemon-reverse-engineering-tools
gfx: fix misuse of export_2bpp_to_png
Merge pull request #57 from yenatch/master

gfx rewrites and 1bpp support