Fixed building on RHEL/CentOS 8. There were three main issues
with compiling on RHEL/CentOS 8:

  1. boost::asio::io_service was deprecated in 1.66. The
     "common/io_service.h" header creates a typedefs io_context
     to io_service if the boost version is greater than or equal
     to 1.66.
  2. boost::asio::basic_stream_socket native() method deprecated
     in 1.47. The version of boost is checked when the 'native()'
     is used and switches to 'native_handle()' if the version is
     greater than 1.47.
  3. Using proj_api.h is deprecated. Added a define to
     "src/CMakeLists.txt" for ACCEPT_USE_OF_DEPRECATED_PROJ_API_H.

Fixes GobySoft#51.