'restrict' is harmful as it encourages the compiler to make dangerous
assumptions while increasing cognitive load on the human programmer.
The extra 1% (or whatever) of performance here is not worth the cost.
char **s not needed to get trailing whitespace trimmed,
and rtrim() does not return anything
if there is leading whitespace in *s in call to string_strip(),
there is less chars left to scan in rtrim().
1. All '*.env' files in an 'environment.d' directory alongside each
potential 'environment' file will be parsed and added to the
environment.
2. For the purposes of configuration merging, an environment definition
exists at one level if either the 'environment' file is defined or
its corresponding 'environment.d' contains any valid '*.env' file.
3. Variable declarations of the form "VARIABLE=", with no following
value, will be written to the environment as empty strings.
