fix build without libsigrokdecode

When built with libsigrokdecode additional headers are automagically included
via the Python.h header. When built without they must included explicitly.
Fix more warnings when building without libsigrokdecode.
man: Update uart decode example syntax

"parity" is no longer a valid option, it's parity_type
manpage: Break line that's too long.

Otherwise "man" will auto-break it and add a confusing dash, etc. etc.
show: Add support for showing PD annotation rows.
show: Cosmetics and consistency fixes.