add lower_case string algorithm

Author: lareii

src/string/lower_case.jule

@@ -0,0 +1,9 @@
+pub fn lower_case(mut string: str): str {
+    for i, c in string {
+        if c >= 'A' && c <= 'Z' {
+            string[i] = 'z' - ('Z' - c)
+        }
+    }
+
+    ret string
+}

test.jule

@@ -16,6 +16,7 @@ use src::string::{
 	is_alpha,
 	is_digit,
 	upper_case,
+	lower_case,
 }
 
 static mut TESTS: TestStack = TestStack.new()
@@ -85,6 +86,10 @@ fn add_tests_string() {
 	TESTS.add("upper_case", fn(): bool {
 		ret upper_case("foO") == "FOO"
 	})
+
+	TESTS.add("lower_case", fn(): bool {
+		ret lower_case("FOo") == "foo"
+	})
 }
 
 fn main() {