This change adds optimized versions of the core memory functions,
relying on 4-alignment, 2-alignment, and the SH4's unaligned move
instruction to (hopefully) attain good performance in all situations.
Since Memallox's newlib port is currently unstable, gint has to
provide some standard functions on its own. Instead of a single
<gint/std.h> header, this commit makes a gint/std directory containing
headers under standard names.