mer - the cmusic merge command

The merge command may be used to accomodate scores which are not given
in time order.  It causes cmusic to read in one or more merge sections,
evaluating p2 and p4 fields as it goes.  Each section is separately
sorted into time order, then the sections are merged into a single,
sorted score.  Example:

    merge;

	    note, gen, pri, and var statements only {MERGE SECTION 1}

	endsec;

	    note, gen, pri, and var statements only {MERGE SECTION 2}

	endsec;

    endmerge;

NOTE: "ins", "mer", "sec", "set" or "ter" statements are treated as
errors within a merge; "com" statements are ignored.

