allow a map[string]interface{} to be provided as the params also

[mzimmerman]

In my use case I have a simple key/value list (not any hierarchy) and a map[string]interface{} is apparently natively supported, just was not exposed publicly -- this change exposes it publicly so that we don't have to create a dynamic struct at runtime using reflect and can instead just send the map

[bobiverse]

I did merged PR, but there was no issue (just no good comments).
There are some basic types, but complex types (like map) is sent through StructParams. Which now is confusing because there is similar func StructToParams.
StructParams will become AnyToParams to avoid confusion

	default:
		if reflect.ValueOf(v).Kind() == reflect.Struct {
			t.params = StructToParams(val)
		} else {
			// any other type try to convert
			t.params = AnyToParams(val)
		}
	}
	```

It will be changed in next release. See: `t.params_test.go`