Add LLaVA support (#2234)

* first commit

* llava

* clippy and fmt

* some fixes

* minor fixes

* remove useless file

* refactor: Remove llava/constants.rs and update llava/mod.rs

* modify variable name

* modify code after clippy

* Minor tweaks.

---------

Co-authored-by: laurent <laurent.mazare@gmail.com>

candle-examples/examples/llava/conversation.rs

@@ -0,0 +1,114 @@
+pub enum SeparatorStyle {
+    Two,
+    Mpt,
+}
+pub struct Conversation {
+    pub system: String,
+    pub roles: Vec<String>,
+    pub messages: Vec<(String, Option<String>)>,
+    pub offset: i32,
+    pub sep_style: SeparatorStyle,
+    pub sep: String,
+    pub sep2: Option<String>,
+    pub version: String,
+}
+
+impl Conversation {
+    pub fn new(
+        system: &str,
+        roles: &[String],
+        offset: i32,
+        sep_style: SeparatorStyle,
+        sep: &str,
+        sep2: Option<&str>,
+        version: &str,
+    ) -> Self {
+        Conversation {
+            system: system.to_string(),
+            roles: roles.to_vec(),
+            messages: Vec::new(),
+            offset,
+            sep_style,
+            sep: sep.to_string(),
+            sep2: sep2.map(|s| s.to_string()),
+            version: version.to_string(),
+        }
+    }
+
+    pub fn conv_chatml_direct() -> Self {
+        Conversation::new(
+            "<|im_start|>system\nAnswer the questions.",
+            &[
+                "<|im_start|>user\n".to_string(),
+                "<|im_start|>assistant\n".to_string(),
+            ],
+            0,
+            SeparatorStyle::Mpt,
+            "<|im_end|>",
+            None,
+            "mpt",
+        )
+    }
+
+    pub fn conv_llava_v1() -> Self {
+        Conversation::new(
+            "A chat between a curious human and an artificial intelligence assistant. The assistant gives helpful, detailed, and polite answers to the human's questions.",
+            &[
+                "USER".to_string(),
+                "ASSISTANT".to_string(),
+            ],
+            0,
+            SeparatorStyle::Two,
+            " ",
+            Some("</s>"),
+            "v1"
+        )
+    }
+
+    pub fn append_message(&mut self, role: String, message: Option<&str>) {
+        self.messages.push((role, message.map(|s| s.to_string())))
+    }
+
+    pub fn append_user_message(&mut self, message: Option<&str>) {
+        self.append_message(self.roles[0].clone(), message);
+    }
+
+    pub fn append_assistant_message(&mut self, message: Option<&str>) {
+        self.append_message(self.roles[1].clone(), message);
+    }
+
+    pub fn get_prompt(&self) -> String {
+        match self.sep_style {
+            SeparatorStyle::Mpt => {
+                let mut ret = String::new();
+                ret.push_str(&self.system);
+                ret.push_str(&self.sep);
+                for (role, message) in &self.messages {
+                    ret.push_str(role);
+                    if let Some(message) = message {
+                        ret.push_str(message);
+                    };
+                    ret.push_str(&self.sep);
+                }
+                ret
+            }
+            SeparatorStyle::Two => {
+                let seps = [self.sep.clone(), self.sep2.clone().unwrap()];
+                let mut ret = String::new();
+                ret.push_str(&self.system);
+                ret.push_str(&seps[0]);
+                for (i, (role, message)) in self.messages.iter().enumerate() {
+                    ret.push_str(role);
+                    if let Some(message) = message {
+                        ret.push_str(": "); // strictly follow the python implementation, otherwise it will cause some minor difference between tokens ^_^
+                        ret.push_str(message);
+                        ret.push_str(&seps[i % 2]);
+                    } else {
+                        ret.push(':')
+                    }
+                }
+                ret
+            }
+        }
+    }
+}