This change is a quick hack solving known issues with URI-encoding in
libkiwix.
This change removes the slash character from the list of URL separator
symbols in URL encoding/decoding utilities, and makes it a symbol that
is safe to leave unencoded.
Effects:
- `urlEncode()` never encodes the '/' symbol (even when it is requested
to encode the URL separator symbols too).
- `urlDecode(str)`/`urlDecode(..., false)` will now decode %2F to '/';
other encoded URL separator symbols are NOT decoded when the second
argument of `urlDecode()` is set to false (which is the default).