Made InvalidHeader error more verbose.

Changed the way we handle TransferEncoding
and added new test cases.

Signed-off-by: cihodar <cihodar@amazon.com>
Signed-off-by: YUAN LYU <lyuyuan92@gmail.com>

src/lib.rs

@@ -121,4 +121,4 @@ pub use crate::response::{Response, StatusCode};
 pub use crate::server::{HttpServer, ServerError, ServerRequest, ServerResponse};
 
 pub use crate::common::headers::{Headers, MediaType};
-pub use crate::common::{Body, Method, Version};
+pub use crate::common::{Body, HttpHeaderError, Method, Version};