Consistently use pointer receivers for core.Number (#375)

Change all occurrences of value to pointer receivers
Add meta sys files to .gitignore
Code cleanup e.g.
- Don't capitalize error statements
- Fix ignored errors
- Fix ambiguous variable naming
- Remove unnecessary type casting
- Use named params

Fix #306

api/distributedcontext/map_test.go

@@ -138,8 +138,8 @@ func TestMap(t *testing.T) {
 			t.Errorf("Expected kv %v, but not found", kv)
 			return true
 		})
-		if len, exp := got.Len(), len(testcase.wantKVs); len != exp {
-			t.Errorf("+got: %d, -want: %d", len, exp)
+		if l, exp := got.Len(), len(testcase.wantKVs); l != exp {
+			t.Errorf("+got: %d, -want: %d", l, exp)
 		}
 	}
 }