Patch by Anish Shah and Aatish Neupane.

This matches the usage of ZipFile and BufferedWriter. This still requires
return values to be bytes() objects.

Also document and test that the write() methods should only access their
argument before they return.

Based on documentation by AM Kuchling.

Check the user warning in test_error_after_default() to not pollute the output,
and check the warning logged into stderr.

Based on patch by Alex Shkop.

Most fixes to Doc/ and Lib/ directories by Ville Skyttä.

instruction decoding.  Based on patch by Demur Rumed.

Patch by Xiang Zhang.