grammar changes:

 - remove old, duplicate sqstring rule that was accidentally left in
   when an updated version was added

 - pull simple grammar out of README.md, into a separate file.  It's not
   interesting to anybody else, so shouldn't be there

 - note context-sensitive rules, such as no duplicate save frame names

 - add section outlining which errors will be reported
change error reporting of loop parser slightly: report
  just position of loop start, not the entire token

add unit tests showing that parser fails inappropriately
  with an exception when the context-sensitive rules are
  violated
oops, didn't update example when fullParse interface was changed