tree-wide: remove Emacs lines from all files This should be handled fine now by .dir-locals.el, so need to carry that stuff in every file.

basic: modernize conf-files.c a bit

basic: include only what we use This is a cleaned up result of running iwyu but without forward declarations on src/basic.

util-lib: introduce dirent-util.[ch] for directory entry calls Also, move a couple of more path-related functions to path-util.c.

util-lib: split out fd-related operations into fd-util.[ch] There are more than enough to deserve their own .c file, hence move them over.

util-lib: split our string related calls from util.[ch] into its own file string-util.[ch] There are more than enough calls doing string manipulations to deserve its own files, hence do something about it. This patch also sorts the #include blocks of all files that needed to be updated, according to the sorting suggestions from CODING_STYLE. Since pretty much every file needs our string manipulation functions this effectively means that most files have sorted #include blocks now. Also touches a few unrelated include files.

build-sys: split internal basic/ library from shared/ basic/ can be used by everything cannot use anything outside of basic/ libsystemd/ can use basic/ cannot use shared/ shared/ can use libsystemd/