Updated the PEG grammar in the docs to match the code.
Added generation of a proper Tcl error code to all parser runtimes
(Tcl, C, generated). Updated all test cases having generated parsers
as their results.

Updated the apps (pt, tools/regenerate_parsers) to use try to properly
capture syntax errors for display.

Updated pt::parse::peg to new PEG grammar and above parse changes.
Made the bench tool a proper script.