add a helper class to "fork" grammars

It takes a template grammar and spits out two `.g4` files, one for
a denting version, and one for a "braced" version. The braces used are
unicode triangles to avoid conflict with typical languages. The idea
is to create two version of the same grammar, one with denting and one
without, so that we can benchmark them. This approach is a bit hacky,
but it's simple and should be enough.
don't need explicit ${FORKER_HEADER} marker

header is always just at the beginnign of the file
bringing indent/dedent tokens to GrammarForker
add a new benchmarking grammar with forks
start benchmark test, refactor util methods
finish first run of benchmark test

I'm getting odd results -- the denter is significantly faster than
the non-denter! I wonder if this is due to my use of multi-byte braces?
change arrows to braces

That didn't do much, but I did notice that the dented code is shorter
than the braced code: 232 chars vs 301. That may be causing the
difference in parse times, so I'll look into that.
rename to remove -Test suffix (so mvn test ignores)
remove extra spaces when converting dent to braces

The token counts are now closer (232 for denter, 187 for braces) and
the times make more sense.
making the dent-to-brace more in line with dented
be a bit more clever about maintaing spaces

Rather than guessing, take a look at the token we're translating, and
use the spacing it implies. This doesn't get braces fully right, but
it's better than we were before!
have the rewriter explicitly indent

it only uses the incoming token's position within each line, and only
for non-dent/nl tokens. For dedents, it explicitly adds indentation
before the braces by keeping track of the nesting count and assuming
two spaces per indent. This is still not perfect, but if the input
source does have two spaces per indent level, we actually get pretty
much exactly what we want. This is now a fair comparison.
reduce number of warmups
put "else" on same line as "if"'s closing brace
add a slightly larger benchmark program
let the tests scale their runs/warmups
adding newlines