Pure Python Release

v1.7.3

• create pure python packaging
• include wheel file
• package as python3 only

v1.7.2

• allow non-integer beam centers
• add badges to docs
• use sphinx-book-theme for docs

v1.7.1

• explicit warning for non-monochrome images in beam_size()
• improve help() messages

v1.7.0

• fix error in identifying major/minor axes in beam_size_plot()