Fixed building on RHEL/CentOS 8.

[cgagner]

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.

Tested on CentOS 7 and CentOS 8.

Fixes #51.

Additional Note:

• The src/CMakeLists.txt defines MOOS_LIBRARIES to be MOOS. This should possibly get changed to using the namespaced version MOOS::MOOS.
• This pull request does not modify the version in the CMakeLists.txt. If accepted, the version should probably get updated to 2.1.15 and a new tag created...

[tsaubergine]

Thanks! This is conceptually very close to my implementation in Goby3:

GobySoft/goby3@997168a

Could you cherry-pick that commit for the relevant parts (io_service)? I'd prefer that goby2 still cleanly merge into goby3.

I would also prefer that "#define ACCEPT_USE_OF_DEPRECATED_PROJ_API_H" be in the actual header, not set by CMake, so that downstream projects don't have to set it in their own build system.

See: GobySoft/goby3@f2bf8e4#diff-44d2cc23f56a2a4368a643e762156c8e

(this #define will also need to be added to https://github.com/GobySoft/goby/blob/2.1/src/moos/moos_geodesy.cpp)

Finally, since this is your first contribution to Goby, could you please sign the CLA by adding your name and email to https://github.com/GobySoft/goby/blob/2.1/AUTHORS and make that part of your PR?

Once you make these changes I'll merge this in. Thanks for your help!