Add support for struct embedding

[matdurand]

We should be able to support

type ToBeEmbedded struct {
	SubParam1 string `bind:"query=sub_param1"`
}

type TestStructWithEmbedded struct {
	Embedded ToBeEmbedded
	Param1   int    `bind:"query=param1"`
	Header1  string `bind:"header=header1"`
}