Release v4.1

I am happy to finally announce a new release! Major changes:

• A new exciting cspan single/multi-dimensional array view (with numpy-like slicing).
• Signed sizes and indices for all containers. See C++ Core Guidelines by Stroustrup/Sutter: ES.100, ES.102, ES.106, and ES.107.
• Customizable allocator per templated container type.
• Updates on cregex with several new unicode character classes.
• Algorithms:
  • crange - similar to boost::irange integer range generator.
  • c_forfilter - ranges-like filtering.
  • csort - fast quicksort with custom inline comparison.
• Support for uppercase flow-control macro names in ccommon.h.
• Create single header container versions with python script.
• Some API changes in cregex and cstr.