Add configured_limits_t type and percolate it to the easy places.
Use default limits for change feeds.

There's no obvious place for it to acquire the user's specified
versions, so we just pick the default :/
Propogate ql::configured_limits_t to everything that needs it
Break configured_limits to their own file
Stub parting optargs in.
Add limits to read_t and write_t.

Tim suggested this, and it seems to be productiev although protocol is failing with a weird error message.
Add copy constructor, since apparently we need it.
These do actually need to be modifiable.
Remove explicit-only copy constructor
We're initializing using an empty global optargs list, so use default
Fix otherwise inexplicable compile errors by making this field nonconst
Propogate read_t & write_t constructor changes
Sketch implementation.

This is nothing better than a sketch, because of the NULL env pointer.
Better sketch.  Let's see if this works.
Lose redundant std::moves
Per @srh, underscore suffix instead of prefix
Expand on why we need a fake, here.
STL iterators grew -> when I wasn't looking
Remove redundant XXX
Set up serialization & unlimited amounts.