[gdf] fix cgs conversion factors

f2cgs was an inverse of what it should be. I've fixed it so now yt-2.x
gives proper results. Output version was bumped from 2.00 -> 2.01
Add script that allows to upgrade h5 output data from 2.00 to 2.01
Merge pull request #62 from Xarthisius/gdf_units_fix

[gdf] fix cgs conversion factors