IBLTMultiset as a regular IBLT, add operations to be abstracted in their own classes

[novakboskov]

Ideally, the IBLT class should be templated with the abstract Adder class. The Adder class should have two concrete classes of which one is a regular decimal adder (considered default) and another one is the modular adder that works for multisets. DecimalAdder and ModularAdder should be very simple classes that only use operator+.

What is the issue with the current implementation?

• It doubles a lot of code and needs complete separate implementations of the sync protocol for IBLT and IBLTMultiset.

Other issues:

• void Communicant::commSend(const IBLTMultiset &iblt, bool sync) is superfluous. If IBLTMultiset inherits from IBLT then why wouldn't IBLT version of commSend work for IBLTMultiset too?
• _insertModular accepts 1 or -1 and does addition and subtraction. That is not a good idea as the function does not return anything and all the positive and negative integers will pass arguments type checking thus making troubles in runtime.