make Range headers strongly typed (again)

From what I can see, the old, good implementation was commented out back
in 2018 during some large refactoring of the whole crate, and 4b42e4f
reenabled the range module,  while replacing the old, strongly typed
implementation with an implmentation that moves parsing of ranges out of
the decoding, into an iterator function. While the implementation that
4b42e4f brought was certainly better than no implementation at all, the
old implementation should've been fixed instead, considering that it was
mostly spec compliant and supported more variants than the back then new
implementation, and it even had tests, which the other one had not.

Sadly, the I had only found the old implementation after writing a
mostly feature complete new implementation, so this wasted a lot of
effort right here. With the old implementation found, and the new and
improved implementation at hand, a consolidated implementation did
arise, now with more documentation, stronger type guarantees and more
test cases then ever.

Signed-off-by: Jan Christian Grünhage <[email protected]>

src/common/mod.rs

@@ -52,6 +52,8 @@ pub use self::pragma::Pragma;
 //pub use self::prefer::{Prefer, Preference};
 //pub use self::preference_applied::PreferenceApplied;
 pub use self::proxy_authorization::ProxyAuthorization;
+pub use self::range::ByteRangeBuilder;
+pub use self::range::ByteRangeSpec;
 pub use self::range::Range;
 pub use self::referer::Referer;
 pub use self::referrer_policy::ReferrerPolicy;