Added "per" division

TODO.md

@@ -2,7 +2,6 @@
  - Reference previous results
  - Minimize parenthesis when printing expressions
  - Sane autoconversion (mi + km)
- - "per" as division?
  - -> as "to"
  - strip_unit function
 

src/evaluate/operator.rs

@@ -16,6 +16,7 @@ pub fn eval_operator(op: &Operator, args: &VecDeque<Token>) -> Result<Token, Eva
 		Operator::ImplicitMultiply |
 		Operator::Sqrt |
 		Operator::Divide |
+		Operator::DivideLong |
 		Operator::Subtract => { panic!() }
 
 		Operator::Negative => {

src/parser/token/operator.rs

@@ -12,6 +12,7 @@ use super::Function;
 #[repr(usize)]
 pub enum Operator {
 	ModuloLong = 0, // Mod invoked with "mod"
+	DivideLong,
 	UnitConvert,
 	Subtract,
 	Add,
@@ -69,6 +70,7 @@ impl Operator {
 			"i*"     => {Some( Operator::ImplicitMultiply )},
 			"%"      => {Some( Operator::Modulo )},
 			"mod"    => {Some( Operator::ModuloLong )},
+			"per"    => {Some( Operator::DivideLong )},
 			"to"    => {Some( Operator::UnitConvert )},
 			"^"|"**" => {Some( Operator::Power )},
 			"!"      => {Some( Operator::Factorial )},
@@ -146,6 +148,7 @@ impl Operator {
 				)
 			},
 
+			Operator::DivideLong |
 			Operator::Divide => {
 				if args.len() != 2 { panic!() }
 				let a = args.pop_front().unwrap();
@@ -232,6 +235,14 @@ impl Operator {
 				);
 			},
 
+			Operator::DivideLong => {
+				return format!(
+					"{} per {}",
+					self.add_parens_to_arg(&args[0]),
+					self.add_parens_to_arg(&args[1])
+				);
+			},
+
 			Operator::UnitConvert => {
 				return format!(
 					"{} to {}",