update README.rst
bump version to 0.6.3
urlrewriter refactor: replace get_abs_url and get_timestamp_url with
get_new_ur() which just calls wburl.to_str and applies rewriter prefix
allows creating a new wburl with any component(s) changed
refactor handlers: simplify handling methods: handle_request() called
for all requests, handle_query() only for url query/calendar, and
handle_replay() only for replay. Improves extensibility of the handling
path