New macro `PRESSED(x)` tests `gMain.newKeys & (x)`. The macro itself
is inoptimal. However, its use is required to match this function.
We suspect this macro may have been implemented globally, hence we
put it in `global.h`. Propagating its use through the remainder of
this project, as well as [Ruby](/pret/pokeruby) and [Emerald](/pret/pokeemerald),
has been left as a to-do item.