feat: modifying functions having iterators as input should be overloaded with functions taking const_iterator

This is what most standard containers are doing today.

By replacing std::deque with boost::circular, I got a few compilation errors...

Prior to C++11, the guideline was to prefer iterator because of some STL API defect in regard to const_iterator but this got fixed in C++11

References:
Effective STL book
item 26: Prefer iterator to const_iterator, reverse_iterator, and const_reverse_iterator

Effective Modern C++ book
Item 13: Prefer const_iterators to iterators