feat(lib): replace types with those from http crate

BREAKING CHANGE: `Method`, `Request`, `Response`, `StatusCode`,
  `Version`, and `Uri` have been replaced with types from the `http`
  crate. The `hyper::header` module is gone for now.

  Removed `Client::get`, since it needed to construct a `Request<B>`
  with an empty body. Just use `Client::request` instead.

  Removed `compat` cargo feature, and `compat` related API.

src/headers.rs

@@ -0,0 +1,85 @@
+use http::HeaderMap;
+use http::header::{CONNECTION, CONTENT_LENGTH, EXPECT, HeaderValue, TRANSFER_ENCODING};
+use unicase;
+
+pub fn connection_keep_alive(headers: &HeaderMap) -> bool {
+    for line in headers.get_all(CONNECTION) {
+        if let Ok(s) = line.to_str() {
+            for val in s.split(',') {
+                if unicase::eq_ascii(val.trim(), "keep-alive") {
+                    return true;
+                }
+            }
+        }
+    }
+
+    false
+}
+
+pub fn connection_close(headers: &HeaderMap) -> bool {
+    for line in headers.get_all(CONNECTION) {
+        if let Ok(s) = line.to_str() {
+            for val in s.split(',') {
+                if unicase::eq_ascii(val.trim(), "close") {
+                    return true;
+                }
+            }
+        }
+    }
+
+    false
+}
+
+pub fn content_length_parse(headers: &HeaderMap) -> Option<u64> {
+    // If multiple Content-Length headers were sent, everything can still
+    // be alright if they all contain the same value, and all parse
+    // correctly. If not, then it's an error.
+
+    let values = headers.get_all(CONTENT_LENGTH);
+    let folded = values
+        .into_iter()
+        .fold(None, |prev, line| match prev {
+            Some(Ok(prev)) => {
+                Some(line
+                    .to_str()
+                    .map_err(|_| ())
+                    .and_then(|s| s.parse().map_err(|_| ()))
+                    .and_then(|n| if prev == n { Ok(n) } else { Err(()) }))
+            },
+            None => {
+                Some(line
+                    .to_str()
+                    .map_err(|_| ())
+                    .and_then(|s| s.parse().map_err(|_| ())))
+            },
+            Some(Err(())) => Some(Err(())),
+        });
+
+    if let Some(Ok(n)) = folded {
+        Some(n)
+    } else {
+        None
+    }
+}
+
+pub fn content_length_zero(headers: &mut HeaderMap) {
+    headers.insert(CONTENT_LENGTH, HeaderValue::from_static("0"));
+}
+
+pub fn expect_continue(headers: &HeaderMap) -> bool {
+    Some(&b"100-continue"[..]) == headers.get(EXPECT).map(|v| v.as_bytes())
+}
+
+pub fn transfer_encoding_is_chunked(headers: &HeaderMap) -> bool {
+    let mut encodings = headers.get_all(TRANSFER_ENCODING).into_iter();
+    // chunked must always be the last encoding, according to spec
+    if let Some(line) = encodings.next_back() {
+        if let Ok(s) = line.to_str() {
+            if let Some(encoding) = s.rsplit(',').next() {
+                return unicase::eq_ascii(encoding.trim(), "chunked");
+            }
+        }
+    }
+
+    false
+}