Reducing/eliminating Boost library dependencies

[karihepola]

OpenASIP uses the Boost library for various functionalities. Some of these are nowadays implemented as part of the C++ standard library, which would allow them to be replaced with standard library functions. For example:

https://en.cppreference.com/w/cpp/filesystem

[Joonari]

Functionalities of the Boost filesystem were replaced with those of std::filesystem in #297. Several other functionalities still depend on Boost, though.