Implementing probability spaces

Replacing core module.
Removing abstract layer from integer module
Some irrelevant docstring mod
Implementing product probability spaces

This has required some modifications in the single probabability space, and
some tools imports.
Init order is name-pspace-func + pfunc

.pfunc is a special method for calculating func over a dicted sample which may
consider a couple of probability spaces affecting and not affecting the rv.
Minor variable name mods
FDRV inits name-pspace-func
PMF may get more than one coordinate

This is in order to allow FDRVs which have a product probability space as their
underlying pspace.

This requires additional treatment in other methods (such as CDF?).
Implementing flatten for FDRV

In addition, a binop may flatten.
Removing real's abstract layer

Plus adding a note for the future.
Rewriting real's binop, removing ppf

.ppf was already defined in superclass.
Removing tricks, adding a warning for op.pow