Added an interactive mode to the query subcommand

Bonjour Guillaume,

I've added an interactive mode to the query subcommand.  It is activated with the -i flag and kmers are read one per line from stdin, the output is flushed.  The rationale for this feature is for using jellyfish as part of a front-end that makes dynamic queries.  A jellyfish process is launched on a DB and, through a pipe, queries can be made without going through the overhead of relaunching jellyfish.