Add circuitpython-munge script

this script can either show the munged version of a Python program,
or show the diff.

Typical output:
```diff
$ circuitpython-munge src/bundle/libraries/helpers/requests/adafruit_requests.py --diff
--- src/bundle/libraries/helpers/requests/adafruit_requests.py
+++ src/bundle/libraries/helpers/requests/adafruit_requests.munged.py
@@ -33,7 +33,7 @@

 """

-__version__ = "0.0.0+auto.0"
+__version__ = "munged-version"
 __repo__ = "https://github.com/adafruit/Adafruit_CircuitPython_Requests.git"

 import errno
@@ -41,7 +41,7 @@

 import json as json_module

-if not sys.implementation.name == "circuitpython":
+if 0:
     from ssl import SSLContext
     from types import ModuleType, TracebackType
     from typing import Any, Dict, Optional, Tuple, Type, Union
```

circuitpython_build_tools/scripts/munge.py

@@ -0,0 +1,27 @@
+import pathlib
+from difflib import unified_diff
+import click
+from ..munge import munge
+
+
+@click.command
+@click.option("--diff/--no-diff", "show_diff", default=False)
+@click.option("--munged-version", default="munged-version")
+@click.argument("input", type=click.Path(exists=True))
+@click.argument("output", type=click.File("w", encoding="utf-8"), default="-")
+def main(show_diff, munged_version, input, output):
+    input_path = pathlib.Path(input)
+    munged = munge(input, munged_version)
+    if show_diff:
+        old_lines = input_path.read_text(encoding="utf-8").splitlines(keepends=True)
+        new_lines = munged.splitlines(keepends=True)
+        output.writelines(
+            unified_diff(
+                old_lines,
+                new_lines,
+                fromfile=input,
+                tofile=str(input_path.with_suffix(".munged.py")),
+            )
+        )
+    else:
+        output.write(munged)

setup.py

@@ -18,5 +18,6 @@
       entry_points='''
         [console_scripts]
         circuitpython-build-bundles=circuitpython_build_tools.scripts.build_bundles:build_bundles
+        circuitpython-munge=circuitpython_build_tools.scripts.munge:main
       '''
       )