wrote more of the compressor and added some tests

test/compress/properties.js

@@ -0,0 +1,25 @@
+keep_properties: {
+    options = {
+        properties: false
+    };
+    input: {
+        a["foo"] = "bar";
+    }
+    expect: {
+        a["foo"] = "bar";
+    }
+}
+
+dot_properties: {
+    options = {
+        properties: true
+    };
+    input: {
+        a["foo"] = "bar";
+        a["if"] = "if";
+    }
+    expect: {
+        a.foo = "bar";
+        a["if"] = "if";
+    }
+}