Support compile-time switches

[huderlem]

Allow compile-time switches to be passed into the poryscript compiler. This will allow things like localization or game version differences.

Idea for syntax:

script LittlerootTown_RivalHouseSign {
    lockall
    checkplayergender
    if (var(VAR_RESULT) == MALE) {
        poryswitch(LANGUAGE) {
            DE: msgbox("Das ist MAY's Haus.")
            FR {
                msgbox("French words.")
                foo(1, 2)
            }
            _:  msgbox("This is any language except German and french.")
        }
    }
    releaseall
}

You would invoke poryscript like this:

poryscript.exe -s LANGUAGE=DE -s GAME_VERSION=RUBY

[huderlem]

text MyText {
    poryswitch(LANGUAGE) {
        DE: "Das ist MAY's Haus."
        FR: format("French words.")
        _:  "Fallback text\n"
             "Still the same text."
    }
}

movement MyMovement {
    poryswitch(GAME_VERSION) {
        RUBY {
           walk_left
           walk_right
        }
        SAPPHIRE: walk_up
    }
}

[huderlem]

3c22421

[martingaldeca]

This seems to me like a very useful thing, but for non technical users add it into the makefile can be difficult. I suggest to add in the readme how to modify the makefile to make this clear. I was trying to open a PR but it seems that it is not possible to open new branches.

I wanted to suggest this change into the README file, just after line 789:

### Add switches to a decomp project

If you want to add any switch to your project automatically, you need to modify the Makefile this way (Note, don't add the `+` symbol at the start of the lines. That's just to show the line is being added.):
```diff
FIX := tools/gbafix/gbafix$(EXE)
MAPJSON := tools/mapjson/mapjson$(EXE)
JSONPROC := tools/jsonproc/jsonproc$(EXE)
SCRIPT := tools/poryscript/poryscript$(EXE)
+ YOUR_SWITCH := YOUR_SWITCH_VALUE
```
```diff
sound/%.bin: sound/%.aif ; $(AIF) $< $@
+ data/%.inc: data/%.pory; $(SCRIPT) -i $< -o $@ -fc tools/poryscript/font_config.json -s YOUR_SWITCH=$(YOUR_SWITCH)
```