adding 'look' command - fetch, then invoke shell in temporary directory

As discussed by ibo2perl6++ PerlJam++ in the #perl6 irc: http://irclog.perlgeek.de/perl6/2014-10-21#i_9543182

This has note been tested on Win32, but it is based on the cpanminus implementation: http://irclog.perlgeek.de/perl6/2014-10-21#i_9543182, so hopefully works ok.