OpenQuake Hazardlib 0.21.0

[Trevor Allen (@treviallen)/Graeme Weatherill (@g-weatherill)]

• Adds Geological Survey of Canada magnitude scaling relations for offshore thrust earthquakes
• Add site adjusted version of Zhao et al. (2006) for application in Cascadia

[Jonathan Griffin (@griffij)/Graeme Weatherill (@g-weatherill)]

• Adds Leonard (2014) magnitude-area scaling relation
• Cleanup of scaling relation test code, removes fragile tests of the get_available_scalerel function

[Michele Simionato (@micheles)]

• Extended the RtreeFilter to work on all sources; removed the Tile class
• Introduced an optional RtreeFilter for fast filtering of the sites by
  point sources, based on the source bounding box

[Graeme Weatherill (@g-weatherill)]

• Adds/Modifies Ry0 and Rx calculator for multi-surface typology using the Generalized Coordinate System (GC2)
• Implements the European GMPE of Kotha et al. (2016), the SaRotD100 GMPE of Hong & Goda (2007) and the Arias Intensity GMPE of Trvasarou et al. (2003)

[Michele Simionato (@micheles)]

• The SourceSitesFilter is now used by default in pmap_from_grp
• Added a simple argument parser in baselib
• Replaced pydoc.locate with a call to importlib to work around a QGIS issue
• Fixed the encode/decode functions in baselib.python3compat

[Daniele Viganò (@daniviga)]

• Added Python 3 compatibility to speedups

[Trevor Allen (@treviallen)/Graeme Weatherill (@g-weatherill)]

• Adds Queen Charlotte strike slip magnitude scaling relation (WC1994_QCSS)