Add command constants to generated code

[lukescott]

Command classes have define parameter values for commands. Rather than defining them with generic types, such as byte, create a enum type.

The switch binary command class for example:

<cmd_class key="0x25" version="1" name="COMMAND_CLASS_SWITCH_BINARY" help="Command Class Switch Binary" read_only="false" comment="">
    <cmd key="0x02" name="SWITCH_BINARY_GET" help="Switch Binary Get" comment="" />
    <cmd key="0x03" name="SWITCH_BINARY_REPORT" help="Switch Binary Report" comment="">
      <param key="0x00" name="Value" type="BYTE" typehashcode="0x01" comment="">
        <valueattrib key="0x00" hasdefines="true" showhex="true" />
        <bitflag key="0x01" flagname="off/disable" flagmask="0x00" />
        <bitflag key="0x02" flagname="on/enable" flagmask="0xFF" />
      </param>
    </cmd>
    <cmd key="0x01" name="SWITCH_BINARY_SET" help="Switch Binary Set" comment="">
      <param key="0x00" name="Switch Value" type="BYTE" typehashcode="0x01" comment="">
        <valueattrib key="0x00" hasdefines="true" showhex="true" />
        <bitflag key="0x01" flagname="off/disable" flagmask="0x00" />
        <bitflag key="0x02" flagname="on/enable" flagmask="0xFF" />
      </param>
    </cmd>
  </cmd_class>

It currently generates:

type Set struct {
	SwitchValue byte
}

It should generate something like:

type SwitchValueType byte

const (
	Off SwitchValueType = 0x00
	On SwitchValueType = 0xFF
)

func (v SwitchValueType) Validate() bool {
	switch (v) {
	case On, Off:
		return true
	default:
		return false
	} 
}

type Set struct {
	SwitchValue SwitchValueType
}

[bjyoungblood]

I looked at doing this, but it's hard to do programmatically due to the flagname parameter. For this specific example, you could split on / and title-case the first match, but there are some command classes where avoiding naming conflicts will be difficult (see https://github.com/gozwave/gozw/blob/master/gen/data/zwave-defs.xml#L8468).

My original intention was for gozw to act as a library that specifically understood zwave, and to create an additional library that was focused on abstracting these types of application-level concerns without requiring much specific knowledge of zwave. I never got around to figuring out how that fits in with everything else, so it's probably worth discussing.