uncrustify.cfg: initial support for notmuch coding style

Uncrustify is a free (as in GPL2+) tool that indents and beautifies
C/C++ code. It is similar to GNU indent in functionality although
probably more configurable (in fairness, indent has better
documentation).  Uncrustify does not have the indent mis-feature of
needing to have every typedef'ed type defined in the
configuration (even standard types like size_t).

This configuration starts with the linux-kernel style from the
uncrustify config, disables aggressive re-indenting of structs,
and fine tunes the handling 'else' and braces.

In an ideal situation, running uncrustify on notmuch code would be
NOP; currently this is not true for all files because 1) the
configuration is not perfect 2) the coding style of notmuch is not
completely consistent; in particular the treatment of braces after
e.g. for (_) is not consistent.

Some fine tuning by Tomi Olilla.