Unicode string iter (#48)

* update string iter to not copy strings

* add rune width

* add missing tests

tests/test_unicode_string.mojo

@@ -0,0 +1,23 @@
+from gojo.unicode import UnicodeString
+from tests.wrapper import MojoTest
+
+
+fn test_unicode_string():
+    var test = MojoTest("Testing unicode.UnicodeString")
+    var s = UnicodeString("𡨸漢𡨸漢")
+    test.assert_equal(s.bytecount(), 14)
+    test.assert_equal(len(s), 4)
+
+    var i = 0
+    var results = List[String]("𡨸", "漢", "𡨸", "漢")
+    for c in s:
+        test.assert_equal(String(c), results[i])
+        i += 1
+
+    test.assert_equal(String(s[:1]), "𡨸")
+    test.assert_equal(String(s[:2]), "𡨸漢")
+    # test.assert_equal(String(s[:-1]), "𡨸漢𡨸漢")
+
+
+fn main():
+    test_unicode_string()

tests/test_unicode_width.mojo

@@ -0,0 +1,20 @@
+from gojo.unicode import string_width, rune_width, UnicodeString
+from tests.wrapper import MojoTest
+
+
+fn test_string_width():
+    var test = MojoTest("Testing unicode.string_width and unicode.rune_width")
+    var ascii = "Hello, World!"
+    var s: String = "𡨸漢𡨸漢"
+    test.assert_equal(string_width(s), 8)
+    test.assert_equal(string_width(ascii), 13)
+
+    for r in UnicodeString(s):
+        test.assert_equal(rune_width(ord(String(r))), 2)
+
+    for r in UnicodeString(ascii):
+        test.assert_equal(rune_width(ord(String(r))), 1)
+
+
+fn main():
+    test_string_width()