Add scripts used to get data.

Hrothvitnir ("fame-wolf", another name for Fenrir) outputs diversity
statistics from posterior sets of trees.
Hydra (named so because it deals with 4 trees at a time) outputs
deltaTMRCA and SPR statistics from posterior sets of trees.
LD_calculator_ChiSqdf does what it says on the tin.

Will add the IPython notebook soon too.