REFACTOR: http yielding

- Centralize yielding in httpProtocol
- Remove yields from handlers and use mprNeedYield
- Remove recursion from httpProtocol
- Eliminate mprYield from all but the blocking APIs
- Add APIs: httpClientConn, httpServerConn, httpRequestExpired, httpStealConnHandle, httpStealSocket, httpAddEof, httpNextQueueFull
- Remove APIs: httpCloseConn
- Rename httpEvent => httpIOEvent, httpPump => httpProtocol
- Changed APIs: httpServiceQueues
REFACTOR: Rename httpMapFile => httpSetFilename, httpMapRequest => httpMapFile
FIX: html escape directory listing filenames.
FIX: auto create ESP cache directory if missing.
FEATURE: Add appweb -N switch as alias for —log stdout:N
TEST: update web sockets unit test to use buffering.
CLEANUP: regen makefiles and fix test appweb.conf
FIX: Old API reference.
TEST: add more form unit tests.