Problem: cache paths are derived by replacing each reserved/filesystem-
path-sensitive char with a `%` char in the original path. With this
method, two different files at two different paths (each containing `%`
chars) can erroneously resolve to the very same cache path in certain
edge-cases.
Solution: derive cache paths by url-encoding the original (path) instead
using `vim.uri_encode()` with `"rfc2396"`. Increment `Loader.VERSION` to
denote this change.
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