Main

Replace boost::regex with std::regex. Goodbye to Boost!

Minor code cleanup. Bump version to v0.5.1.

Replace boost::filesystem with std::filesystem. Replace
boost::program_options with CLI11. Rename ProtectedAndSynchronizedQueue
to ProtectedQueue. Fix error with JPEG_REGEX. Bump version to v0.5.0.

Update PCA CMakeLists.txt. Build libpackjpg as a dependent external
project.

Use computed library path for install.