feat: support sqrt

other roots may prove to be quite a challenge,
since I would need to parse the syntax `root(base, value)`

src/nodes/evaluate.rs

@@ -40,6 +40,8 @@ fn collapse_toplevel(nodes: &mut Vec<Node>, mut end: usize) {
     {
         match &mut nodes[start..end][index + 1] {
             Node::Number(n) => match variant {
+                Function::Sqrt => n.sqrt_mut(),
+
                 Function::Sine => n.sin_mut(),
                 Function::ArcSine => n.asin_mut(),
                 Function::Cosine => n.cos_mut(),

src/nodes/from_str.rs

@@ -32,6 +32,8 @@ impl FromStr for Function {
     type Err = String;
     fn from_str(s: &str) -> Result<Self, Self::Err> {
         match s {
+            "sqrt" => Ok(Self::Sqrt),
+
             "sin" => Ok(Self::Sine),
             "asin" => Ok(Self::ArcSine),
             "cos" => Ok(Self::Cosine),

src/nodes/mod.rs

@@ -40,6 +40,8 @@ enum Operator {
 
 #[derive(Debug, Copy, Clone, PartialEq)]
 enum Function {
+    Sqrt,
+
     Sine,
     ArcSine,
     Cosine,