This function will compare two Annotations, Ann1 and Ann2, according to
their Span sets.
Return Value:
This function returns -1 if Ann1 is lower than
Ann2, i.e. Ann1 spans a text range that starts earlier than all the
text ranges spanned by the Ann2 Annotation. If the two Annotations span
the same text ranges, zero is returned. Finally, 1
is returned if Ann1 is greater than Ann2, i.e. when Ann2 spans a
text range starts earlier than all the text ranges spanned by the Ann1
Annotation. In case of an error, a value equal or greater than 10 will
be returned and an error message will be left at the current Tcl
interpreter (CDM_Interp).