Fix sourcemaps in JSXTransformer for Firefox

Fixes #1725
Merge pull request #1801 from zpao/jsxtransformer-sourcemaps

Fix sourcemaps in JSXTransformer for Firefox
Add docblocks and consistent styling to JSXTransformer
Merge pull request #1802 from zpao/jsxtransformer-cleanup

Jsxtransformer cleanup
Docs: added note about `renderComponent()` requirement