Add ranking parameters to search in command line interface

[jldevezas]

This can either be passed using:

• The command line argument --params=par1:xpto,par2:coisa;
• Or a properties file passed through --params=bm25.properties.

Where bm25.properties contains:

k1=1.2
b=0.75

[jldevezas]

We should also add this to the new interactive query mode, for example using:

\ranking bm25

And setting parameters using:

\set k1 1.2
\set b 0.75

Also a reset to default parameters would be nice. Maybe simply use \unset?

\unset k1
\unset b