Refactors

unpack 4-bit tiles when quest is loaded ff01c741b

This reduces CPU usage by ~3%.

Previously, 4-bit tiles were only unpacked just before being drawn. Unpacking means converting into a format ready for drawing, which is somewhat slow to do in functions as hot as tile drawing. Now, when a qst is loaded all 4-bit tiles are unpacked in memory. When saving a qst the reverse happens. This change has no impact on the qst file format.
avoid copy when drawing tile without any transformation 973303a3c

This reduces CPU usage by ~7%.
make get_qr faster by unpacking the bits ahead of time 990eb380b

This reduces CPU usage by ~5.5%.