Fix auth handling during OfferCreate (RIPD-414)
Make bind_handler variadic ctor explicit
Add HTTPHeaders::build_map
Enable asynchronous handling of HTTP-RPC (RIPD-390)
* Activate async code path
* Tidy up HTTP server code
* Use shared_ptr in HTTP server
* Remove check for unspecified IP
* Remove hairtrigger
* Fix missing HTTP authorization check
* Fix multisocket flags in RPC-HTTP server
* Fix authorization failure when no credentials required
* Addresses RIPD-159, RIPD-161, RIPD-390
Set version to 0.26.1
Merge branch 'release-next' into release

Conflicts:
	src/ripple/module/app/paths/cursor/ForwardLiquidity.cpp
	src/ripple/overlay/tests/peer_info.test.cpp
	src/ripple/unity/http.h