Merge branch 'syntax/unary-operators' into 'master'

Add some unary operator tests

See merge request !22

syntax/PrefixIncrement.invalid.mj

+public Foo {
+
+    public static void main(String[] args) {
+        --a;
+    }
+
+}

syntax/UnaryExpressions.mj

+class Foo {
+
+    public static void main(String[] args) {
+        - -a;
+        -(-a);
+        -(-(a));
+
+        !a;
+        !(!a);
+        !!a;
+        !!!!a;
+        -!!!!a;
+    }
+
+}