Add mpfr 3.1.6 and add license information
Add mpfr 3.1.6 and add license information

Add the mpfr license, switch to sha256, and add 3.1.6 release

Signed-off-by: Tim Smith <764ef62106582a09ed09dfa0b6bff7c05fd7d1e4@chef.io>

aerobase/omnibus-software,chef/omnibus-software,mattray/omnibus-software,higanworks/omnibus-software,aerobase/omnibus-software,mattray/omnibus-software,aerobase/omnibus-software,higanworks/omnibus-software,chef/omnibus-software,chef/omnibus-software,higanworks/omnibus-software,aerobase/omnibus-software,aerobase/omnibus-software,mattray/omnibus-software,chef/omnibus-software,chef/omnibus-software,chef/omnibus-software,mattray/omnibus-software,mattray/omnibus-software,higanworks/omnibus-software