Use enums instead of numbers.

[nkrapivin]

Most of the state-machine stuff in STT is using numbers to represent states, which isn't very convenient.
(have to open the state reference, and considering how awful GM:S 1.4's IDE is... well...)
It's better to rewrite all of it to use enums, a good example of this is the objMusic refactor in the release/1.1.2 branch.

[nkrapivin]

Should do that while porting the game to GMS 2. But not now. (now - 1.1.2)