Restructure spec file
    
    The ordering wasn't quite right. Also made some other minor quality of
    packager's life improvements.
    
    - Drop `module_name` var (only used in one place)
    - Put BRs in main package
    - Move `_description` to a more suitable place
    - Don't enumerate single source
    - Stop building for i686
    - Use `%forgeautosetup` instead of `%autosetup`
    
    [skip changelog]