class constants added and class instances for integral types

docs/Real.md

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+# Real built-in class
+
+Class that supports double-precision math. Woks much like double in other languages. We honor no floats, so it is '
+Real'.
+
+It's class in Ling is `Real`:
+
+    (π/2)::class
+    >>> Real
+
+you can use it's class to ensure type:
+
+    1.71::class == Real
+    >>> true
+
+## Member functions
+
+| name         | meaning                            | type |
+|--------------|------------------------------------|------|
+| `roundToInt` | round to nearest int like round(x) | Int  |
+|              |                                    |      |
+|              |                                    |      |
+|              |                                    |      |
+|              |                                    |      |
+|              |                                    |      |