DOC: typos
DOC optional -> optimal
DOC optional -> optimal
typos throughout the codebase
TST: special: account for floating point limitations in cos-integral test
Merge pull request #3200 from argriffing/moretypos

MAINT: fix typos
Merge pull request #3204 from pv/mpmath-test-fix

TST: special: account for floating point limitations in cos-integral test