Fix support for namecheap

[Grub4K]

This PR fixes the 2 problems with the current namecheap support and also updates the README.md to reflect that.

---

The first problem stems from the good and nochg strings no longer getting sent back, making inadyn think the request failed (while it might not have).
The example in the README.md on the other hand will always succeed, since true is always in the response, even if it failed. Refer to the examples below.

I have decided to replace both with a check for <ErrCount>0</ErrCount>.

faulty response

<?xml version="1.0" encoding="utf-16"?>
<interface-response>
  <Command>SETDNSHOST</Command>
  <Language>eng</Language>
  <ErrCount>1</ErrCount>
  <errors>
    <Err1>Passwords do not match</Err1>
  </errors>
  <ResponseCount>1</ResponseCount>
  <responses>
    <response>
      <Description>Passwords do not match</Description>
      <ResponseNumber>304156</ResponseNumber>
      <ResponseString>Validation error; invalid ; password</ResponseString>
    </response>
  </responses>
  <Done>true</Done>
  <debug><![CDATA[]]></debug>
</interface-response>

successful response

<?xml version="1.0" encoding="utf-16"?>
<interface-response>
  <Command>SETDNSHOST</Command>
  <Language>eng</Language>
  <IP>XXX.XXX.XXX.XXX</IP>
  <ErrCount>0</ErrCount>
  <errors />
  <ResponseCount>0</ResponseCount>
  <responses />
  <Done>true</Done>
  <debug><![CDATA[]]></debug>
</interface-response>

---

The second problem is username and hostname being swapped in NAMECHEAP_UPDATE_IP_REQUEST causing it to send domain=%h, host=%u instead of domain=%u, host=%h. While we can work around this by swapping username and hostname in the config, this means we cannot specify multiple hostnames.

I have swapped the two fields and think it is worth this breaking change for ease of use, especially since the plugin is currently broken and people couldn't be relying on it anyways.

current option (custom provider)

custom namecheap {
  username    = domain.tld
  password    = mypass
  ddns-server = dynamicdns.park-your-domain.com
  ddns-path   = "/update?domain=%u&password=%p&host=%h&ip=%i"
  ddns-response = "<ErrCount>0</ErrCount>"
  hostname = { "@" "www" }
}

current option (plugin)

provider default@namecheap.com:1 {
  username = "@"
  password = mypass
  hostname = domain.tld
}
provider default@namecheap.com:2 {
  username = "www"
  password = mypass
  hostname = domain.tld
}

new option

provider default@namecheap.com {
  username = domain.tld
  password = mypass
  hostname = { "@" "www" }
}

[troglobit]

Well I don't have any way to test, so I'll just trust you. This does however make you de facto maintainer of the namecheap plugin 😉