Base+Manpages: Add basic GML documentation

First draft of GML documentation, just to get things started.

Base/usr/share/man/man5/GML-Define-property.md

@@ -0,0 +1,20 @@
+## Name
+
+GML Property Definition
+
+## Description
+
+How to register property to a widget.
+
+**LIbGUI** widget definitions contain macros that define the properties that can be used for a given widget.
+
+However, widgets also understand properties defined by their parents. Such as  `x`, `y`, `name`, etc.
+
+## Examples
+
+```cpp
+REGISTER_ENUM_PROPERTY(
+        "button_style", button_style, set_button_style, Gfx::ButtonStyle,
+        { Gfx::ButtonStyle::Normal, "Normal" },
+        { Gfx::ButtonStyle::Coolbar, "Coolbar" });
+```