Make externally visible some generic code useful to create

Make externally visible some generic code useful to create
and implement services over tcp and/or tcp-tls.

This commit is nothing more than moving structure definitions
(and documentation) from main/http.c to include/asterisk/http.h
(temporary location until we find a better place), and removing the
'static' qualifier from server_root() and server_start().

The name change (adding the ast_ prefix as a minimum, and then
possibly a more meaningful name) is postponed to future commits.

Does not apply to other versions of asterisk.

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@48324 65c4cc65-6c06-0410-ace0-fbb531ad65f3