A few bug fixes

Fixed bug in shortestPaths.
Now allow approxCholSddm to accept params.
Removed PyPlot from REQUIRE so that it will pass JuliaCIBot tests.

Bug fix in approxCholSddm

Only minor changes: fixed a bug in approxCholSddm that made it unusually slow.

v0.2.0

This version is compatible with Julia 0.6.0