Ugrid2 dev

[daltonkell]

Updated UgridChecker

After creating a dependency graph for the feature checks, the checker has
been re-written to run more efficiently and with more logical, readable
steps. 1-D and 2-D meshes are checked for their features, while development
for fully unstructured, 3D meshes is needed. The checks also come complete
with tests. Other changes are as follows:
  - renamed UgridChecker10 to UgridChecker
  - renamed test file
  - updated checks.md
  - updated ugrid.cdl test file
  - edited setup.py accordingly

[daltonkell]

This also addresses #6 (closing that issue).