[tech] make some items public

[patochectp]

No description provided.

[woshilapin]

There is a bunch of new exposed API which are not hidden behind the feature-flag gtfs_parser:

• gtfs::EquipmentList (which was in gtfs::read::EquipmentList before and gtfs::read is private)
• calendars::manage_calendars (which was pub(crate) but is now pub and module calendars is pub)
• read_utils::FileHandler (and friends read_utils::PathFileHandler and read_utils::ZipFileHandler) which I really would not expose, at least not without a feature (another file_handler feature?)
• read_utils::read_objects, read_utils::read_collection and read_opt_collection, not a fan of exposing those either, but it doesn't make sense to hide it behind gtfs_parser or file_handler features

Idea - maybe it's not a gtfs_parser feature that we need but 2 features: gtfs and parser. You would hide all of gtfs::read behind #[cfg(all(feature = "gtfs", feature = "parser"))] and hide the read_* functions of read_utils behind #[cfg(feature = "parser")]?

[woshilapin]

I was thinking it would be nice to add some documentation about the 2 new introduced features into the preamble of src/lib.rs (see how it's already done for the existing features).

[patochectp]

I was thinking it would be nice to add some documentation about the 2 new introduced features into the preamble of src/lib.rs (see how it's already done for the existing features).

I told myself the same thing

[woshilapin]

I would mention that the exposed API are not stable and that using this is experimental. I'm not expecting us to be as careful about the stability here that for the rest of the exposed API. What do you think?

[patochectp]

done in 6f11bef