The expectation deduplication algorithm called |Array.prototype.splice|
to eliminate each individual duplication, which was slow. This caused
problems with grammar/input combinations that generated a lot of
expecations (see #377 for an example).
This commit replaces the algorithm with much faster one, eliminating the
problem.
The |found| property wasn't very useful as it mostly contained just one
character or |null| (the exception being syntax errors triggered by
|error| or |expected|). Similarly, the "but XXX found" part of the error
message (based on the |found| property) wasn't much useful and was
redundant in presence of location info.
For these reasons, this commit removes the |found| property and
corresponding part of the error message from syntax errors. It also
modifies error location info slightly to cover a range of 0 characters,
not 1 character (except when the error is triggered by |error| or
|expected|). This corresponds more precisely to the actual situation.
Fixes#372.
