Handle special characters on pull

[wayword-dev]

Was testing out pull when testing my whirly dependency PR and discovered that it doesn't handle spaces in file names correctly. This PR resolves that.

Example error (with site name redacted):

$ neocities pull
😿  Retrieving files for my-site                               

A fatal error occurred :-(
bad URI(is not URI?): "https://my-site.neocities.org/file with space.html"

As far as I can tell, there is no escaping in the list endpoint in the API:

• https://github.com/neocities/neocities/blob/0531a1d85fd2b0d7b1fa333669230f867dd83f89/models/site.rb#L1236-L1264
• https://github.com/neocities/neocities/blob/0531a1d85fd2b0d7b1fa333669230f867dd83f89/app/api.rb#L18-L43

[kyledrake]

Thank you