Compilation time improvements. (#52)

* Precompiled header for all common library headers (with cmake 3.16rc3).
* Divided cmake build into shared libraries.
* Added gold linker support.
* Separated websockets lambda expressions to an independent file.

src/crypto.cpp

@@ -1,5 +1,4 @@
-#include <cstdio>
-#include <iostream>
+#include "pchheader.hpp"
 #include "crypto.hpp"
 #include "util.hpp"