Base+Manpages: Add basic GML documentation

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

Base/usr/share/man/man5/GML-Syntax.md

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+## Name
+
+GML Basic Syntax
+
+# Description
+
+How to write GML using proper syntax.
+
+## Basic Syntax
+
+Each widget begins with `@GUI::`, with the name of the widget following. To define the properties of this widget, we follow with curly brackets and a list of properties.
+
+## Properties
+
+A property's `value` is required to be in the property's set `type`:
+
+- `int`
+- `bool`
+- `string`
+- `readonly_string`
+- `enum`
+- `font_weight`
+- `text_alignment`
+- `text_wrapping`
+- `rect`
+- `size`
+- `margins`
+
+Properties are never ended with `;` or `,`, and the property name is never enclosed in quotes or double quotes.
+
+Properties are always surrounded by curly brackets (e.g. `{}`). If no properties are set however, no brackets are required.
+
+## Examples
+
+```gml
+@GUI::Widget {
+    name: "my_first_widget"
+}
+```