Possible fix for several syntax-related crashes as well as for `use syntax mylang` not functioning correctly.

Crashes were caused by infinite recursion in DaoParser_ErrorX2 and DaoParser_ErrorX3. Use statement breakage was due to not seeking ahead far enough in the token list after parsing the use statement. This may not be the correct fix for that; there may be a need to actually do some parsing to figure out how many tokens forward to seek. But this worked in my tests.

- Added $STR() to stringify a macro value (i.e., $STR($ID1))
- Added $CAT() to concatenate macro values (i.e., $CAT($ID1 '_Helper'))
- Fixed a bug where a value failing to be found in a ZERO_OR_ONE group nested in another ZERO_OR_ONE group would cause the higher-level group to also report a non-match
- Fixed a bug where a plain identifier in the last section of a group could cause a failed match in some circumstances (i.e., { [ $ID1 '=' '4' ';' ] 'io' '.' 'writeln' '(' '{' "hello world" '}' ')' ';' } would fail to match correctly.

Put them in different commits because I'm just copying and pasting the files into github directly, because I haven't set up a local git workspace yet on my box.

…ntax:

   load "modulename.ext"

Add: new vm instruction DVM_UNTAG for untagging a value of type "X|none"...