Merge pull request SciTools#1695 from pelson/v1.8.1_bump

Updated version to v1.8.1.

Merge pull request SciTools#1673 from marqh/version181rc

release candidate 1

Merge pull request SciTools#1631 from rhattersley/v1.7.4

Update release date.

Merge pull request SciTools#1630 from marqh/date18

release date

Merge pull request SciTools#1622 from bjlittle/rc-2

Merge pull request SciTools#1602 from bjlittle/rc-1

Bump the version for the release candidate.

Merge pull request SciTools#1582 from rhattersley/v1.7.x_whats_new

v1.7.4rc1 what's new

Merge pull request SciTools#1499 from lbdreyer/tag_v1.7.3

Bump version to v1.7.3

Merge pull request SciTools#1493 from dkillick/release_candidate

Bump version to v1.7.3-rc.1

Merge pull request SciTools#1406 from dkillick/release_v1.7.2

Release v1.7.2