string: Add implementation of translate() method.

As MicroPython doesn't have str.translate() method, here it's implemented
as string module function.

string/metadata.txt

@@ -1,3 +1,3 @@
 srctype=micropython-lib
 type=module
-version=0.0.1
+version=0.1

string/setup.py

@@ -6,7 +6,7 @@ from setuptools import setup
 
 
 setup(name='micropython-string',
-      version='0.0.1',
+      version='0.1',
       description='string module for MicroPython',
       long_description="This is a module reimplemented specifically for MicroPython standard library,\nwith efficient and lean design in mind. Note that this module is likely work\nin progress and likely supports just a subset of CPython's corresponding\nmodule. Please help with the development if you are interested in this\nmodule.",
       url='https://github.com/micropython/micropython/issues/405',

string/string.py

@@ -8,3 +8,19 @@ hexdigits = digits + 'abcdef' + 'ABCDEF'
 octdigits = '01234567'
 punctuation = """!"#$%&'()*+,-./:;<=>?@[\]^_`{|}~"""
 printable = digits + ascii_letters + punctuation + whitespace
+
+
+def translate(s, map):
+    import io
+    sb = io.StringIO()
+    for c in s:
+        v = ord(c)
+        if v in map:
+            v = map[v]
+            if isinstance(v, int):
+                sb.write(chr(v))
+            elif v is not None:
+                sb.write(v)
+        else:
+            sb.write(c)
+    return sb.getvalue()