v5.19.0

What's new

• Added US Customary units for square foot (sq_ft), square mile (sq_mi), and square chain (sq_ch).

What's changed

• Changed symbol of units cb (M) and cb (US) to metric_cb and us_cb in length.
• Changed symbol of unit hp (M) to metric_hp in power.
• Changed symbol of unit cwt (US) to us_cwt in weight.