The expectation langauge is LL(1) but the scanner does not support true
lookahead
This change adds a true LL(1) token stream and rewrites the parser in terms of
it.
Also clean up the error handling and use the behaviour to fix all the broken
edge cases, and then change the tests to cover the now correct behaviour.
Change-Id: If3d602cda490ed2f4732efce400eb8eabce8a8ec
Reviewed-on: https://go-review.googlesource.com/c/151998
Run-TryBot: Ian Cottrell <iancottrell@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rebecca Stambler <rstambler@golang.org>
895048a75e