Failing unit tests for passing children to <Table>

This is a set of failing tests for passing <Tr> children to the <Table>
instead of a data array.
Merge branch 'master' of github.com:glittershark/reactable into feature/additional_apis
Making nested Trs work
Making tests a little more robust by checking for thead
Merge pull request #1 from lofiinterstate/feature/additional_apis

Make it possible to nest Trs in <Table> definition
Update README with new nested Tr API
Merge branch 'feature/additional_apis'