#6 Gibbs sampling

[Lee Katz]

Add Gibbs sampling for GeneMark. The gibbs sampling script crashes in GeneMark and so it is turned off (gmsn.pl --motif=0). However, it should be turned on by default to improve accuracy of start sites (to turn off, use config setting genemark_rbs=0). To do so, use Andrey's implementation of gibbs.pl. Gibbs should always be used when GeneMark is used.