working tile example with simple test.
before fixing test failure related to missing indices
before fixing test failure related to missing indices
working tiling/chunking with tests
added slice arguments to definition.py
slices passed to ocgoperations
ocgis/test/test_operations.py:Test.test_as_url failing
remove _in_url=False from SliceRow
before modify nc converter to have method returning empty open dataset object
before fixing index error related to schema building
working chunking example test.
Merge branch 'dev' into tiling

Conflicts:
	src/ocgis/test/test_simple.py
TestTile now inherits from TestBase
before making memory allocation requirements less for file_only operation
before removing file_only from engine.py
removed file_only from calc, etc.
moved alterations to operations commands for NetCDF
shifted possible bounds dimension names to constants.py
empty nc converter working for simple tests. added constansts.py file.
working tiling example with reasonable performance. before adding an iterator option to calculations.