Erddap-python

- Releasing a stable version of erddap-python, growing community backed.
- Added slicing capabilities to ERDDAP_Griddap_Dimension classes.
- Added special methods and properties to ERDDAP_Griddap_Dimension type 'time'
- Validation of opendap request of griddap datasets.
- Added a new way to request griddap subsets using regular slice objects, using integer indexing or real dimensions values, The methods `setSubsetI`, `setSubset`.

- Bug fix: MLD timeseries parsing for ERDDAP version 2.12 wasn't working.

- Added parse status support for ERDDAP version 2.12, new metrics: nunique_users_since_startup. New columns for MLD timeseries: R_toomany and open_files_percent.
- Included `__version__` number property in erddapClient class

- Added methods to parse ERDDAP status.html page, results are stored in DataFrames and scalars. Method is available in erddapClient.ERDDAP_Server.parseStatusPage()
- Bug fix method setConstraints()

- Added the methods getxArray and getncDataset that can get subsets of ERDDAP griddap datasets and return xarray or netCDF4.Dataset objects
- Parsing methods for griddap querys of extended opendap format, to integer indexes equivalents.

- Removed os.path.join usage to build url strings, that caused the search operations to fail on windows.
- Added test on windows os.