Migrate core source files to C++. Add yaml-cpp project as dependency (#2207)

By updating to this commit, Linux users have to regenerate Makefiles by re-running the configure script.

* Added yaml-cpp project as a 3rdparty library
* Migrated source files core to C++
* Updated configure scripts
* Make Linux installations compile *.cpp files
* Made server components' main source file C++
* Also made headers CPP-aware.

* Added basic C wrapper for yaml-cpp library
* YAML-node path is delimited by periods.
* Basic integer types and string are supported.
* Strings returned from this wrapper have to be freed with malloc.h::aFree
* Arrays (sequence) is supported with iterator wrapper.
* Remember to free every wrapper you create!

* Add yaml-cpp as dependency of common project
* Made the repo not ignore *.yml files

Thanks to @aleos89 and @Lemongrass3110.

3rdparty/yaml-cpp/src/memory.cpp

@@ -0,0 +1,26 @@
+#include "yaml-cpp/node/detail/memory.h"
+#include "yaml-cpp/node/detail/node.h"  // IWYU pragma: keep
+#include "yaml-cpp/node/ptr.h"
+
+namespace YAML {
+namespace detail {
+
+void memory_holder::merge(memory_holder& rhs) {
+  if (m_pMemory == rhs.m_pMemory)
+    return;
+
+  m_pMemory->merge(*rhs.m_pMemory);
+  rhs.m_pMemory = m_pMemory;
+}
+
+node& memory::create_node() {
+  shared_node pNode(new node);
+  m_nodes.insert(pNode);
+  return *pNode;
+}
+
+void memory::merge(const memory& rhs) {
+  m_nodes.insert(rhs.m_nodes.begin(), rhs.m_nodes.end());
+}
+}
+}