Allow to transform camel case properties into snake case field names

[anti-social]

It is really boring to explicitly name fields like:

class UserDoc : Document(transformCamelToSnakeCase = true) {
    val userId = int("user_id")
    val firstName = text("first_name")
    val lastName = text("last_name")
}

class UserDoc : Document(transformCamelToSnakeCase = true) {
    val userId = int()
    val firstName = text()
    val lastName = text()
}

assert UserDoc.userId.getFieldName() == "user_id"
assert UserDoc.firstName.getFieldName() == "first_name"
assert UserDoc.lastName.getFieldName() == "last_name"