Make mpfr3 and mpfr3-devel subpackages.
    
    Also:
    - Drop the compat-libmpc package; nothing in Fedora needs it
    - Update project URL
    - Add a -doc subpackage to hold the GFDL-licensed content
    - Drop unnecessary texinfo BR
    - Drop ldconfig_scriptlets; this version cannot appear in distros that need it
    - Make sure there are no rpaths and that -Wl,--as-needed takes effect