[output] Rename output* to react*
[output] Rename output* to react*

Summary:
Eventually simple-markdown will be able to output either html
or react. This change paves the way for that by changing
`output*` functions to be `react*` functions.

Depends on D16645

Test Plan: `make test`

Reviewers: alex

Reviewed By: alex

Differential Revision: https://phabricator.khanacademy.org/D16646

Khan/simple-markdown,Radivarig/simple-markdown