Release 1.2.3

Version update release: officially supported/tested Python versions 2.7, 3.7--3.10

Conda numkit package available now from conda-forge channel (maintained by @njzjz).

What's Changed

• updated tested Python versions (dropped 3.6, added 3.10 and 3.11); note that 3.6 still works but is not tested anymore
• use main branch instead of master #27
• fixed deprecated/removed np.float in numkit.fitting.linfit() (#28)

Full Changelog: release-1.2.2...release-1.2.3