configure.ac: use -Wall -Wextra
**/*.[ch]: massive reformatting

Full code reformatting using:
$ indent --linux-style **/*.[ch]
src/afuse.c: fix user_options, silence all warnings

user_options was missing a field in its static initialization.
ChangeLog -> NEWS: renaming, consistent formatting

Renaming follows the libabc "guidelines":
https://git.kernel.org/?p=linux/kernel/git/kay/libabc.git;a=blob;f=README;h=b4bed;hb=HEAD#l193
README: remove maintainer information, change URI
HACKING: refer to github, specify indentation, fix typos