Port data: url parsing to Rust

This uses the data-url crate.  One change in behavior is that data-url
is strict about data: URLs having a MIME-type chunk in them.  This
will be an apparent regression from issue #152, which requested that
image data be sniffed if a data: URL doesn't have a MIME-type.

However, https://fetch.spec.whatwg.org/#data-urls indeed indicates
that data: URLs without a MIME-type are invalid.

This removes the test files for issue #152, since they are expected to
fail now.
3 jobs for data-uri in 8 minutes and 21 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test
passed #149921
fedora test

00:07:35

 
  Lint
manual #149923
allowed to fail manual
clippy
passed #149922
rustfmt

00:00:46