globalize macros

[truj]

Add a pre-parsing run to the MidicaPL parser, only for parsing MACRO definitions.
Then a macro can be called before it is defined.

[truj]

Probably we need more than 2 parsing runs.
At least the chords should be parsed before so that a not-existing chord definition inside of a macro is no problem.
As a side effect, the chord definitions will also be allowed after usage.
Also the first instrument block has to be parsed before the macros.
That's needed in order to detect the usage of undefined channel numbers inside or outside of macros.
All following instrument blocks must be parsed later in order to continue supporting instrument changes.
DEFINE commands must be parsed before everything else.