minor cleanup.
factor out "alt".
checkpoint: major refactoring to use continuations instead of return values. 20 tests back online so far.
another checkpoint.
repeat.
hook up repeat and reduce!
use the trampoline in repeat() to avoid stack overflow, and catch any repeats that don't make progress.
add and use GLL cache.
bugfixes and new tests.
add another test to verify left recursion. :)
remove dropPrefix.
one more test.
update readme!
to-done.
Merge branch 'continuations'