Adding arrow functions

test/compress/harmony.js

@@ -0,0 +1,37 @@
+arrow_functions: {
+    input: {
+        (a) => b;  // 1 args
+        (a, b) => c;  // n args
+        () => b;  // 0 args
+        (a) => (b) => c;  // func returns func returns func
+        (a) => ((b) => c);  // So these parens are dropped
+        () => (b,c) => d;  // func returns func returns func
+        a=>{return b;}
+        a => 'lel';  // Dropping the parens
+    }
+    expect_exact: "a=>b;(a,b)=>c;()=>b;a=>b=>c;a=>b=>c;()=>(b,c)=>d;a=>{return b};a=>\"lel\";"
+}
+
+arrow_function_parens: {
+    input: {
+        something && (() => {});
+    }
+    expect_exact: "something&&(()=>{});"
+}
+arrow_function_parens_2: {
+    input: {
+        (() => null)();
+    }
+    expect_exact: "(()=>null)();"
+}
+
+regression_arrow_functions_and_hoist: {
+    options = {
+        hoist_vars: true,
+        hoist_funs: true
+    }
+    input: {
+        (a) => b;
+    }
+    expect_exact: "a=>b;"
+}