Implement cross-platform POSIX path normalization function for establishing ELF relationships

[nightlark]

The ELF relationships code currently uses os.path.normpath to cleanup and normalize paths, however the behavior of this function is different on Windows than POSIX systems tested (including macOS). This leads to the unit tests for ELF relationships failing on Windows systems.

The description of the Clean function in Go describes a working normalization function for that would be suitable for this, with the exception of a "//" appearing at the start of a path remaining intact. A few examples of this special behavior:

os.path.normpath("/") -> "/"
os.path.normpath("//") -> "//"
os.path.normpath("///") -> "/"
os.path.normpath("////") -> "/"
os.path.normpath("/..") -> "/"
os.path.normpath("/../") -> "/"
os.path.normpath("//../") -> "//"
os.path.normpath("//a//b/c///d") -> "//a/b/c/d"
os.path.normpath("///a//b/c///d") -> "/a/b/c/d"

The Python docs for the os.path.normpath function can be found at https://docs.python.org/3/library/os.path.html#os.path.normpath and they link to the IEEE Standard on pathname resolution

This fix will also make CI tests pass for #7.