New formula: Radx

The Radx C++ package was developed at NCAR to provide support for the
new CfRadial radar data format, and to provide translation between
common radar data formats.

It provides useful tools for handling radar imagery. With proper dependencies, it installs smoothly on its own configure script with llvm-g++. But clang++ compiler, picked up default by Homebrew, failed to build some C++ codes. Maybe clang does more strict compilation. `fails_with` phrase has been added for a workaround.