Support import files as modules (i.e. import only once)

examples/other.odin

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+add :: proc(a, b: int) -> int {
+	return a + b;
+}

examples/test.odin

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+import "other"
+
+TAU :: 6.28;
+PI :: PI/2;
+
+main :: proc() {
+	x : int = 2;
+	x = x * 3;
+
+	y := add(1, x);
+}