Changed premake.lua to work with mingw.

Implemented array operations, not perfect but ok for tonight. closes #89

tests/mini/arrayops2.d

@@ -0,0 +1,10 @@
+void main()
+{
+    int[4] a = [1,2,3,4];
+    int[4] b = [5,6,7,8];
+    a[] += b[];
+    assert(a[0] == 6);
+    assert(a[1] == 8);
+    assert(a[2] == 10);
+    assert(a[3] == 12);
+}