add ddlpy dependency and enable testcases

[veenstrajelmer]

• move KWK scripts to separate repos #210
• Create ddlpy 0.3.0 release ddlpy#56
• add ddlpy as (optional) dependency
• remove need for git install from example script (remove comment at import statement)
• enable test_ddlpy_to_hatyan on github (and fix assertion)
• Expand and generalize ddlpy_to_hatyan() #212
• add convert_HWLWstr2num testcase
• update hatyan example notebook with ddlpy data
• updat ddl example script
• remove ddl-access part from readme