feat: add more constructors for operator (#33)

* feat: add constructor for the norm (`∥`) operator

* feat: add more operator constructors

src/elements/mo/dict.rs

@@ -16,6 +16,11 @@ impl Operator {
         Self::from("\u{22C5}")
     }
 
+    /// Create a '¨' operator.
+    pub fn double_dot() -> Self {
+        Self::from("\u{00A8}")
+    }
+
     /// Create a '∗' operator.
     pub fn asterisk() -> Self {
         Self::from("\u{2217}")
@@ -191,6 +196,11 @@ impl Operator {
         Self::from("\u{2309}")
     }
 
+    /// Create a '≔' operator.
+    pub fn assign() -> Self {
+        Self::from("\u{2254}")
+    }
+
     /// Create a '=' operator.
     pub fn eq() -> Self {
         Self::from("\u{003D}")
@@ -450,4 +460,9 @@ impl Operator {
     pub fn larrow() -> Self {
         Self::from("\u{2190}")
     }
+
+    /// Create a '~' operator.
+    pub fn tilde() -> Self {
+        Self::from("\u{007E}")
+    }
 }