Revise OPTIONS.md

Revise OPTIONS.md

  - The STD_CDEFINES build-time variable was dropped when the build
    system was migrated to Automake.  CPPFLAGS is the variable which
    should now be used for setting preprocessor macros.

  - Sort the list of preprocessor macros which affect BIND behavior.
    Remove ISC_BUFFER_USEINLINE from the list as it can be controlled
    using its relevant ./configure option (--enable-buffer-useinline).
    Rename NS_RUN_PID_DIR to NAMED_RUN_PID_DIR to match the source code.

  - Tweak Markdown formatting.