Adds the script name to error messages.

- Stored in the global state object
- Displays (repl) for the repl
- Similar format as the v8/d8 executable. Node.js displays additional
  information that we don't currently have available (function names,
  etc.), although that'd be nice later.
- Currently it's only possible to execute one file at a time, but
  this should eventually be more useful when other files can be sourced.
Fixes object literal and block ambiguity

- Follows the requirements in 12.4
- Additions to the grammar test suite.
- Repairs older grammar tests and adds a test-grammar to the Makefile.
- All the examples from the WAT talk should now work as expected
  (well, according to spec. They're not really what I'd call expected ;)