gitignore: allow gitignore to ignore most dot file

Nowadays, most of the editor use files or directories begin with dot to
store some settings. So let git ignore these files and directories to
reduce potential mistakes.

Add dot match to ignore any editor file and there are two exceptions:
- .gitignore
- .clang-format

Signed-off-by: Inochi Amaoto <inochiama@outlook.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Anup Patel <anup@brainfault.org>