Update ref-01-top-level-api.md

Added docs for `React.isValidClass` and `React.isValidComponent`. 

Still missing top level api:

* `constructAndRenderComponent`
* `constructAndRenderComponentById`
* `withContext`
changed type info. added descriptor to descriptions
Merge pull request #2010 from nw/patch-1

Update ref-01-top-level-api.md