Rounding branch lengths of phylogenetic tree to two decimal digits.

As the mutation probability tables already are rounded to two decimal digits
this should not affect PhyloFun's accuracy at all, but significantly speed it
up, because many trees will have much less unique branch lengths once they are
rounded to two decimal digits.
Merge branch 'round_branch_lengths' of github_groupschoof:groupschoof/PhyloFun into round_branch_lengths

Conflicts:
	src/runPhyloFun.R