swift-package-manager

Clean up `Path` by removing `pathSeparatorCharacter` as a constant.  It
gave the appearance of separation-of-concerns, but in reality, it could
not be set to any other character and still have everything work, and
besides, it's not the kind of constant where people will look at the
occurrence of `"/"` in the code and wonder what on earth is special
about slash characters in relation to paths; because of the prevalence
of slash as path separator, this is one of those rare cases in which the
literal itself is actually more readable and clear than a fancy name.