Refactor KeyboardButtonPollType

- Make it enum
- Rename `ButtonRequest::KeyboardButtonPollType` => `<_>::poll`

src/types/keyboard_button.rs

@@ -49,7 +49,7 @@ impl KeyboardButton {
 pub enum ButtonRequest {
     Location,
     Contact,
-    KeyboardButtonPollType(KeyboardButtonPollType),
+    Poll(KeyboardButtonPollType),
 }
 
 /// Helper struct for (de)serializing [`ButtonRequest`](ButtonRequest)
@@ -97,7 +97,7 @@ impl<'de> Deserialize<'de> for ButtonRequest {
             RawRequest {
                 poll: Some(poll_type),
                 ..
-            } => Ok(Self::KeyboardButtonPollType(poll_type)),
+            } => Ok(Self::Poll(poll_type)),
             _ => Err(D::Error::custom(
                 "Either one of `request_contact` and `request_location` fields is required",
             )),
@@ -123,7 +123,7 @@ impl Serialize for ButtonRequest {
                 poll: None,
             }
             .serialize(serializer),
-            Self::KeyboardButtonPollType(poll_type) => RawRequest {
+            Self::Poll(poll_type) => RawRequest {
                 contact: None,
                 location: None,
                 poll: Some(poll_type.clone()),

src/types/keyboard_button_poll_type.rs

@@ -1,25 +1,18 @@
 use serde::{Deserialize, Serialize};
 
+/// This object represents type of a poll, which is allowed to be created and
+/// sent when the corresponding button is pressed.
 #[derive(Clone, Debug, Eq, Hash, PartialEq, Serialize, Deserialize)]
-pub struct KeyboardButtonPollType {
-    poll_type: String,
-}
-
-impl KeyboardButtonPollType {
-    pub fn new<S>(poll_type: S) -> Self
-    where
-        S: Into<String>,
-    {
-        Self {
-            poll_type: poll_type.into(),
-        }
-    }
-
-    pub fn poll_type<S>(mut self, val: S) -> Self
-    where
-        S: Into<String>,
-    {
-        self.poll_type = val.into();
-        self
-    }
+#[serde(rename_all = "snake_case")]
+#[serde(tag = "type")]
+pub enum KeyboardButtonPollType {
+    /// If [`Quiz`] is passed, the user will be allowed to create only polls in
+    /// the quiz mode.
+    Quiz,
+    /// If [`Regular`] is passed, only regular polls will be allowed.
+    Regular,
+    /// If [`Any`] is passed, the user will be allowed to create a poll of any
+    /// type.
+    #[serde(rename = "")]
+    Any,
 }