Deprecating Bond support for EOL platforms and toolchains

[bhardwajs]

Bond is currently supporting Ubuntu 14.04 with Clang 3.8 and g++ 5.4 and VS 2017 on Windows. Ubuntu 14.04 is past support as is VS 2017. Should we update the dependencies to?

• Ubuntu 20.04 and the versions of Clang & GCC it ships with
• VS 2019 atop Server 2019
  My read is that the versions of gcc/clang/MSVC would support C++ 17. Should we bump up to C++ 17?

We can also Boost dependency to require version 1.73 or later which was released on Apr 28, 2020 almost two years ago (https://www.boost.org/users/history/).

For .Net, we can set support surface to

• .Net Framework 4.8+
• .Net Core 3.1
• .Net 5+

[chwarr]

All the minimums proposed here LGTM.