webdav_server: make quit/disconnect handlers debug-only, don't export quit/disconnect url constants
build system: add libwebdav_server_fs.a to list of .PHONE targets
webdav_server: remove fields for stop_cb and stop_ud since they are no longer used
webdav_server: implement "wire allocator" for {webdav,http}_server, related minor bug fixes, improvements.

The "wire allocator" is a memory allocator that is used to allocate
memory that will be used to hold data that is tranmitted over the
wire, e.g. the socket.

The main application for is a server that transmit sensitive data
over the wire. This allows them to have greater control over how
that memory is allocated and deallocated, e.g. special memory regions,
clearing all memory after use.
http_helpers: print correct date despite timezone of current system