Install library, increment version, document macros

[rouson]

1. Increment version to 2.0.0 in fpm.toml
2. Document the new option to invoke assert via a C-preprocessor macro.
3. Update fpm.toml to install the lib assert.a static library.
4. Work around fpm bug + gfortran bug blocking example.
5. Move assert_macro.h to the new include/ subdirectory so that #include "assert_macros.h" statements no longer need to have a hardwired path.