Switch to CMake. Allows faster compilation and simplification of the
Makefile.

Switched libwslay to a static InstallDev library. Allows further
simplification of the Makefile and a smaller size when used with h2o.

Signed-off-by: Rosen Penev <rosenp@gmail.com>

Wslay is a WebSocket library written in C. It implements the protocol version 13
 described in RFC 6455. This library offers 2 levels of API: event-based API and
 frame-based low-level API. For event-based API, it is suitable for non-blocking
 reactor pattern style. You can set callbacks in various events. For frame-based
 API, you can send WebSocket frame directly. Wslay only supports data transfer
 part of WebSocket protocol and does not perform opening handshake in HTTP.

Signed-off-by: James Taylor <james@jtaylor.id.au>