hopefully-improvments to top-level help processing.

incomplete/imperfect, but now you can do at least 'boda mode mode_arg --help' and get the expected results. it should be eqivalent to using the existing/original 'boda help mode mode_arg' syntax (but more standard / handier when editing command lines manually). note that this isn't documented yet, and only works for one level of mode_arg. that is 'boda mode mode_arg=(sub_arg) --help' (still) doesn't work, just as with the prior 'boda help mode ...' syntax.
add b,e dim_t range version of nda_reduce
use range version of nda_reduce to propertly calc reductions per-image in copy_batch_to_img().

removed corresponding FIXME/assert().
use fixed/complete copy_batch_to_img to replace dup'd code in conv_pyra