Expression parser: add TOK_ASSIGNMENT, enable vector indexing on output variable (y). This will allow null-padding of mapped signals when mapped to partial vectors, as well as assignment to possible additional variables in the future.
Expression parser: build typestring for evaluated expressions will nulls for missing vector elements.
Handle null-padded signal updates at receiving device. Switched to using generic OSC typestring handler since details of null-padding cannot be known auntil runtime.
Use null-padding for default linear/calibration expressions in cases when dest_len > src_len.
Fixed bug initializing has_complete_value flags for new signals.
Expression parser/evaluator: allow multiple sub-expressions for e.g. setting different vector elements/ranges.
Expression parser: eliminate TOK_QUESTION since it was really handled by TOK_OP, use bitflags more efficiently in token type enum.
Re-enabled instance updates, but switched to explicit tagging of instance property in message using @instance label as discussed long ago on the mailing list. Instance release messages now require OSC NIL types for each vector element.
Fixed some more instance-sending syntax.
Cleaning up signal handlers & obsolete typestrings; Fixed soem more instance message formatting.
Added some vector signals to testquery and testreverse.
Merge branch 'vector-indexing' into output-vector-indexing

Conflicts:
	src/connection.c
Do not check link scope with NULL map.
Expression parser: enable vector builder left of assignment operator for e.g. output swizzling.
Expression parser: additional checks for bad syntax.
Expression parser: enabled filter history initialization for output (y) - for now initialization expressions must appear first.
Expression parser: added more expression syntax tests to testparser.
testparser: added scientific notation test.
Expression parser: re-order sub-expressions as necessary so that history initialization expressions are evaluated first (these expressions will be skipped in subsequent evaluations).
Expression parser: enabled user-defined variables in expression.