Fix #2. Finish implementing Range.

Covers error and edge cases and fully tested now.

test/range/floating_point.wren

@@ -0,0 +1,31 @@
+// Ordered range.
+IO.print((2..5).from) // expect: 2
+IO.print((3..3).from) // expect: 3
+IO.print((0..3).from) // expect: 0
+IO.print((-5..3).from) // expect: -5
+IO.print((-5..-2).from) // expect: -5
+
+// Backwards range.
+IO.print((5..2).from) // expect: 5
+IO.print((3..0).from) // expect: 3
+IO.print((3..-5).from) // expect: 3
+IO.print((-2..-5).from) // expect: -2
+
+// Exclusive ordered range.
+IO.print((2...5).from) // expect: 2
+IO.print((3...3).from) // expect: 3
+IO.print((0...3).from) // expect: 0
+IO.print((-5...3).from) // expect: -5
+IO.print((-5...-2).from) // expect: -5
+
+// Exclusive backwards range.
+IO.print((5...2).from) // expect: 5
+IO.print((3...0).from) // expect: 3
+IO.print((3...-5).from) // expect: 3
+IO.print((-2...-5).from) // expect: -2
+
+// TODO: Test toString.
+// TODO: Non-number RHS.
+// TODO: Non-integer RHS.
+// TODO: Range iteration.
+// TODO: Empty or negative ranges.