clang-format: formalize some of the spacing rules

clang-format: formalize some of the spacing rules

There are some spacing rules that we follow in the project and it makes
sense to formalize them:
* Ensure there is no space inserted after the logical not '!' operator.
* Ensure there is no space before the case statement's colon.
* Ensure there is no space before the first bracket '[' of an array.
* Ensure there is no space in empty blocks.

Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>