feat: path functions is_abs and abs_path

[wassup05]

User facing functions added are:

• is_abs(path): returns a logical indicating if the path is absolute.
• abs_path(path [, err]): returns the absolutized version of the path.

is_abs does pure string manipulation checking if

• on POSIX systems, path starts with /
• on Windows systems it is either an UNC path or starts with a drive letter like C:\

abs_path performs a syscall to get the current working directory and then joins it to the path, returning the joined path

Prior Art

os.path.abspath (Python)
os.path.isabs (Python)

[sebastian-mutz]

Thanks, @wassup05!
I'm wondering if is_abs_path may be better to use. While "path" is the first thing many will think of from context, it is entirely implied. Even in the use statement stdlib_system, only: is_abs, it's not visible (c.f. Python's os.path.isabs).

[wassup05]

I had that in mind too @sebastian-mutz, and I have changed it now.

[sebastian-mutz]

LGTM with the recent change, @wassup05. Many thanks.

[perazz]

what happens if p is already an absolute path on input?

[perazz]

the is_abs_path function only tests the form of a path specification, not the fact that it must actually exist in the filesystem. So I wonder if giving these functions the same name as is_file, is_directory etc., that instead test the actual filesystem, wouldn't be confusing for some. Also, do other library implementations only check the form, or do they require the actual path to exist?