support multiple variables in request dataset #294

Multiple variables from a target may be passed to the "variable"
argument of "RequestDataset". If "None" is provided for the variable
argument, then the target data object will be searched for variables
to be processed provided they have time and space dimensions.
improved CF support for history attribute #257

For netCDF output, a string representation of "OcgOperations" is
appended to the global history attribute. If there is no operations,
then the release and time are appended only.

closes #257
doc changes
doc changes
doc changes
implement string parsing for calculations #285

String representations of function expressions is now supported for
the "calc" argument to "OcgOperations". Includes doc changes.
added ipython notebooks to examples
uri missing in source metadata files #298

URI is now appropriately passed to Inspect when creating a source
metadata file. This also includes some refactoring of Inspect to
better handle different combinations of instance arguments.

closes #298
ipynb changes
ipynb changes
ipynb changes
remove output directory if process fails #177

If an operation fails, the created output directory is no appropriately
removed.

Closes #177
ipynb changes
added checklist
Rename REALEASE_CHECKLIST.org to RELEASE_CHECKLIST.org
Update RELEASE_CHECKLIST.org
Update RELEASE_CHECKLIST.org
Update RELEASE_CHECKLIST.org
1. Minor changes to test to account for long running test code.
2. Removed bounds search and made sure the target dataset must
   declare bounds explicitly.
3. Added unit tests for get_iter.
4. Minor change to wrap where polygons are now passed as an explicit
   list.
Merge branch 'next' of https://github.com/NCPP/ocgis into next