Merge r1753712 from trunk:

add basic h2: and h2c: backend proxy examples

Submitted by: Hank Ibell <hwibell gmail.com>
Committed by: covener




git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1753713 13f79535-47bb-0310-9956-ffa450edef68