Create ddlpy 0.3.0 release

[veenstrajelmer]

• optional: Update repos to current standards #32
• move to Deltares Github organisation #22
• repair docs #62
• only test on ubuntu-latest, saves some co2
• improve docs #68
• remove requirements.txt and references to it #66
• what happens if tstart and tstop are the same (test for all public functions)
• return empty dataframe instead of none if no measurements #74
• restore Makefile in root
• request pypi rights for ddlpy and rws-ddlpy
• rename pypi package from rws-ddlpy to ddlpy (reserved on pypi) >> already done in pyproject.toml
• update pypi link in readme button
• improve docs again #69
• add link to waterwebervices >> updates to readme. In case of unexpected behaviour, check this first
• readme: update links to parallel/netcdf example script
• add pip uninstall rws-ddlpy -y suggestion to readme, besides pip install ddlpy
• fix TODO in pyproject.toml
• add xarray[io] to pyproject.toml (optional dep)
• add below steps to contributing.rst
• bump the versionnumber with bumpversion minor
• update HISTORY.rst and add a date to the current release heading
• rename package to rws-ddlpy again, pypi does not accept ddlpy it since it is to similar to another package name (ddipy)
• also change in readme (incl buttons, installation howto) and pyproject.toml (package name), more?
• create tag and release on github, should automatically create release on pypi