Add a new version of the freespace command which doens't need autoclean or prot

[RPGHacker]

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Add a new version of the freespace command which takes an arbitrary identifier and doesn't need an autoclean or prot to prevent freespace leaks.

Example:

org $00xxxx
    jsl NewCode

    ; ...

freespace "MyPatch"
    NewCode:
    ; ...

The returned freespace in this case would write a RATS tag, followed immediately by its identifier (in this case "MyPatch") as a 0-terminated ASCII string. Upon applying a patch twice and encountering such a freespace command, Asar could simply search the ROM for all RATS tags that are followed by that exact identifier and clean those areas.

Alternative idea: I'm not sure if having a freespace command automatically clean stuff is desirable. As an alternative, we could add a new autoclean command which takes an identifier and does exactly what I've just described. In any case this makes prot unncessary and (presumeably) makes autoclean more reliable and less complicated.