added cordex regular grid options

[larsbuntemeyer]

• added cordex-regular table.
• modify create_dataset to handle non rotated grids.
• add tests.

[codecov-commenter]

Codecov Report

Merging #54 (d741ced) into master (3c4118d) will decrease coverage by 3.03%.
The diff coverage is 53.19%.

@@            Coverage Diff             @@
##           master      #54      +/-   ##
==========================================
- Coverage   81.32%   78.29%   -3.04%     
==========================================
  Files          18       19       +1     
  Lines         707      857     +150     
==========================================
+ Hits          575      671      +96     
- Misses        132      186      +54     

Flag	Coverage Δ
unittests	78.29% <53.19%> (-3.04%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
cordex/tables/_resources.py	76.78% <ø> (-8.40%)	⬇️
cordex/core/domain.py	75.22% <53.19%> (-6.75%)	⬇️
cordex/cmor/__init__.py	100.00% <0.00%> (ø)
cordex/tables/__init__.py	100.00% <0.00%> (ø)
cordex/tutorial.py	65.67% <0.00%> (ø)