Route parsing fails on empty name tag.

[dvanherbergen]

In route.rs, the name of the route is marked with allow_empty false.
This cause file parsing of routes with an empty tag to fail.
According to the GPX spec, name is optional and there's no minimum length specified making it nullable, so shouldn't allow_empty be set to true?

gpx/src/parser/route.rs

Line 31 in 7ad83e3

route.name = Some(string::consume(context, "name", false)?);