Ndbc-api

Summary of core changes:
* Improve the default response format of `available_realtime` to return a list of the modes supported by a given station. `full_response=True` returns the URLs for available station, optionally as a dataframe.
* Update the parameters in API methods to reflect the migration from the `netCDF4` package to the `xarray` package.
* Expose `xarray` keyword arguments to the `save_xarray_dataset` method.

Bugfixes:
* None noted; some documentation updates to better reflect what parameters are used.

Future improvements:
* None noted.

Summary of core changes:
* Add python 3.12 support in CI
* Improve `setup.py` and `pyproject.toml`
* Include installation instructions for conda (from `conda-forge`) and installation from source
* Improved the flow of examples in the overview notebook
* Added a new `CONTRIBUING.md` which describes how to run tests and submit new features or requests.

Bugfixes:
* Fixed an example in the overview notebook which incorrectly formatted the lat-lon coordinates of an example buoy.
* Improved the descriptions on how to run tests, adding a new `CONTRIBUTING.md`

Future improvements:
* Include station metadata for `get_data` queries in which a single station is requested with `use_opendap=True`
* Align flag, parameter, and method names in light of the migration from `netCDF4` to `xarray`
* Expose more of the xarray API for some common internal operations such as serializing netCDF4 data retrieved from the THREDDS API.

Core Changes:
* Migrated from `netCDF4` library to `xarray` and `scipy`

Bug Fixes:
* Corrected sign in overview notebook example longitude

Future Improvements:
* Include station metadata in single-station `get_data` calls with `use_opendap=True`
* Update the flags and method names to adopt `xarray` naming conventions

Bug Fixes:
* Improved timestamp parsing for some NDBC Data Service modalities

Future Improvements:
* Note noted

Major Changes:
* Added `netcdf4` file support through the `get_data` method when passing the flag `use_opendap=True`

Minor Changes:
* updated tests
* improved `overview.ipynb` documentation to reflect new `netcdf4` support

Bug Fixes:
* None noted

Future Improvements:
* Note noted

Major Changes:
* Update `api.stations()`, `api.nearest_station(...)` and `api.radial_search(...)` to include all of the ~1380 active stations which are tracked by the NDBC data service.
* Added `api.historical_stations()` which returns the historical and current station deployments, with one row for each station, deployment period tuple.

Minor Changes:
* updated tests
* improved `overview.ipynb` documentation

Bug Fixes:
* Issue 40 (return all active stations) addressed in this PR

Future Improvements:
* Issue 40 (support netcdf data export) will be addressed in a subsequent release