Need to preperly escape regexp pattern

[Pilatuz]

The code generator is unable to handle the following regexp pattern:

"name": {
  "type": "string",
  "pattern": "^[0-9a-zA-Z`]+$"
}

The problem here is in ` (U0060) character. The code generator builds the validation helper as:

"{{ .NameSpace }}Pattern = regexp.MustCompile(`" + pattern + "`)"

and contains incorrect escaped Go string if pattern contains U0060 character inside.
Need to properly escape regexp pattern!

[Pilatuz]

also need to escape %, otherwise error message became incorrect because it embeds pattern in format string.

If regexp pattern is 0-9%v then we will have:

message:  fmt.Sprintf(`must match '0-9%v' but got %q`, *m.Name),