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/conf.cpp

@@ -1,15 +1,4 @@
-#include <cstdio>
-#include <iostream>
-#include <fstream>
-#include <unordered_set>
-#include <sodium.h>
-#include <rapidjson/document.h>
-#include <rapidjson/schema.h>
-#include <rapidjson/istreamwrapper.h>
-#include <rapidjson/ostreamwrapper.h>
-#include <rapidjson/prettywriter.h>
-#include <boost/filesystem.hpp>
-#include <boost/algorithm/string.hpp>
+#include "pchheader.hpp"
 #include "conf.hpp"
 #include "crypto.hpp"
 #include "util.hpp"