support Fragments

[mgeorgehansen]

React and Preact both have "Fragment" components, which don't render any wrapper tags but simply delegate rendering to their children. This makes components more composable in contexts where tags have a nesting context (e.g. <li> must be a direct descendant of a <ol> or <ul>).

Unfortunately the TypeScript compiler does not support a custom pragma for React's <></> fragment syntax yet, though this is on track for release soon (see microsoft/TypeScript#38720), but we can provide a Fragment component in the meantime e.g. <Fragment><li>1</li></Fragment>.

[mgeorgehansen]

Closed by #10