feat(wpcarro/simple-select): Support basic Scanner class

...alongside a small REPL to quickly test the functionality.

Change-Id: I3c2b3f060d82cd49488e00dec9b72f7b23e2b666
Reviewed-on: https://cl.tvl.fyi/c/depot/+/5337
Reviewed-by: wpcarro <wpcarro@gmail.com>
Autosubmit: wpcarro <wpcarro@gmail.com>
Tested-by: BuildkiteCI

users/wpcarro/scratch/simple-select/main.py

@@ -0,0 +1,13 @@
+from scanner import Scanner
+
+def tokenize(x):
+  s = Scanner(x)
+  return None
+
+def main():
+  while True:
+    x = input("> ")
+    print(tokenize(x))
+
+if __name__ == "__main__":
+  main()