fixes for feedback method
add info method to all samplers
mh: always use (rerun) to initialize

No other transition type should have to worry about
handling a no-choice-available case.
fix slice sampler for integer dists
clip slice bounds to support, improve error messages
improve errors
only warn about out-of-range once
added vprintf, more consistent debugging output
update observe tests to run
slice, enumerative-gibbs error on structural choice
update and expand asia tests
more tests