api rationalization add cmake switch to export old api wrappers

This is off by default, use

 -D LWS_WITH_OLD_API_WRAPPERS=1

on cmake to get the old api names exported from the library as wrappers
around the new api names.

This allows the library to continue to be compatible with apps that are
not rebuilt with the new libwebsockets.h api compatibility defines.

Signed-off-by: Andy Green <andy.green@linaro.org>