tests: Add unicode test.

tests/unicode/unicode.py

+# Test a UTF-8 encoded literal
+s = "asdf©qwer"
+for i in range(len(s)):
+    print("s[%d]: %s   %X"%(i, s[i], ord(s[i])))
+
+# Test all three forms of Unicode escape, and
+# all blocks of UTF-8 byte patterns
+s = "a\xA9\xFF\u0123\u0800\uFFEE\U0001F44C"
+for i in range(-len(s), len(s)):
+    print("s[%d]: %s   %X"%(i, s[i], ord(s[i])))
+    print("s[:%d]: %d chars, '%s'"%(i, len(s[:i]), s[:i]))
+    for j in range(i, len(s)):
+        print("s[%d:%d]: %d chars, '%s'"%(i, j, len(s[i:j]), s[i:j]))
+    print("s[%d:]: %d chars, '%s'"%(i, len(s[i:]), s[i:]))
+
+# Test UTF-8 encode and decode
+enc = s.encode()
+print(enc, enc.decode() == s)