Contribution Function Update

• A few bug fixes to keys that weren't previously included in the CdfLoader pickles (due to them not being in the FCHROMA documentation!).
• Significant module restructuring
• New matsplotslib and utils submodules to contain the Contribution Function code and associated machinery (xt_calc etc.).
  This stuff will be documented soon (tm)

Initial Github release

Sufficient for loading and performing basic analysis of Radyn simulations when using the rest of the Scientific Python ecosystem. The lazy mode works well. More features coming soonish.