Turn ConsensusParams into a Linelist

One of our dir auth operators tried to set consensusparams on two different lines, and it turns out that the config option is a string, so if you set it twice, you get a log complaint like "Option 'ConsensusParams' used more than once; all but the last value will be ignored."

The reason we should support splitting your consensusparam across multiple lines is because we added the ability to split your torrc across multiple files. So we should be able to have a "default" set of config options, and then another file that adds to them. I was on my way to designing some sort of shell script hack for him but then I realized it's way better to just do it right in Tor. Plus it's a super short patch. :)