`%%LIBDIR%%` in `down.top` needs to be escaped

[nojb]

This is because on Windows it is common for %%LIBDIR%% in

https://github.com/dbuenzli/down/blob/e3a4f38e02bf75fd0206d97dc74c6a5c26342023/src/down.top#L9

to contain backslashes, which need to be escaped (eg by using String.escaped) in

https://github.com/dbuenzli/down/blob/e3a4f38e02bf75fd0206d97dc74c6a5c26342023/pkg/pkg.ml#L20

[dbuenzli]

~~Isn't it rather the #directory directive implementation which should escape ?~~

Forget about that.

[dbuenzli]

@MisterDA can you please try with opam pin topkg --dev to confirm that @nojb's suggestion fixes the problem.

Not sure why this got stuck for so long.

[MisterDA]

Can confirm that it works!

[dbuenzli]

Thanks!