Refactor index key validation and normalisation.
Merge pull request #74 from rhattersley/refactor-keys-normalisation

Refactor index key validation and normalisation.
Add ConstantArray(), zeros() and ones().
Merge pull request #75 from rhattersley/zeros

Zeros and ones functions.
Check ArrayStack/LinearMosaic elements are Arrays.
Update test for improved engine behaviour.
Merge pull request #81 from rhattersley/validate-stack-mosaic

Check ArrayStack/LinearMosaic elements are Arrays.
Merge pull request #80 from rhattersley/update-test

Update test for improved engine behaviour.
ENH: Added N-dimensional Biggus stack support
Merge pull request #76 from cpelley/ndim_big_stack

ENH: Added N-dimensional Biggus stack support
Added array casting to Elementwise and Aggregation like operations.
Review actions.
Merge pull request #83 from pelson/numpy_as_input

Added array casting to Elementwise and Aggregation like operations.
Added mdtol support for biggus.mean()
Removed default val for mdtol from Handlers
tests for mdtol
Merge pull request #86 from esc24/mdtol_for_mean

Mdtol for mean
ENH: Implemented max, min and sum operators