The base URI is ignored for requests that include a host.
WebClient exposes UriBuilder (rather than UriBuilderFactory) for
per-request URI building based on the base URI. That provides
full control to add or replace components of the base URI.
Leave only one static, no-arg build() method for access to a Builder.
URI-related preferences are now exposed on the builder itself.
Improve Javadoc with base URI examples.
