Get rid of fake indexing

I'm not convinced of the utility.
Remove lazily
Remove branch_and_merge
Remove collect
Remove keep

It's not useful in Lua, where nil terminates loop.
Add lazily lib

Gives you lazy coroutine iterator versions of map, filter, etc based on
transducers.
Export apply_to

It's useful for writing other pipe functions.
Change lazily -> transform

Also fix function args
Export exports
Fix bad upvalue reference to transduce
Fix collect with reference to reduce
Fix bug with returning message from reduce

Could cause accidental silent halting of reduction if a function passed
multiple return values through step.

Now we only halt on reduced msg and we never return that msg from
reduce.

This means we don't have a msg channel, but I'm ok with that.
Use ... instead of arg

arg was deprecated in 5.1.
Remove lazily