v0.20.0

Toward stability...

This release does not really introduce breaking changes, nor add new features. It however fixes a lot of small and not so small issues.

router: better support for hash mode
router: update app if parameterized route changes
router: properly react on hashchanges
component: solve tricky concurrency issue (with various concurrent renderings)
component: fix many issues with internal component reconciliation algorithm
router: properly handle popstate event
component: make t-model work with select tags (for initial non empty rendering)
component: make t-model work with sub state keys
qweb: allow recursive templates t-calls