Remove terminal newline from quad.Quad stringer

This is the conventional implementation of a fmt.Stringer.

Also went through and fixed up some lint.
Rename Check-ish -> Contains-ish

Contains[*] indicates what the check is for.

[*] I considered Has/Have, but settled on Contains to avoid confusion
with the HasA iterator.
Merge pull request #90 from kortschak/stringer

Remove terminal newline from quad.Quad stringer
Merge pull request #92 from kortschak/names

Rename Check-ish -> Contains-ish