headers are case-insensitive, correct docblock types

src/Request.php

@@ -190,6 +190,7 @@ public function formatHeaders()
  */
  public function setHeader($key, $value)
  {
+ $key = strtolower($key);
  $this->headers[$key] = $value;
 
  return $this;
@@ -204,6 +205,8 @@ public function setHeader($key, $value)
  */
  public function getHeader($key)
  {
+ $key = strtolower($key);
+
  return isset($this->headers[$key]) ? $this->headers[$key] : null;
  }
 
@@ -281,7 +284,7 @@ public function getOption($key)
  *
  * @param string $user
  *
- * @return mixed
+ * @return static
  */
  public function setUser($user)
  {
@@ -295,7 +298,7 @@ public function setUser($user)
  *
  * @param string $pass
  *
- * @return mixed
+ * @return static
  */
  public function setPass($pass)
  {
@@ -376,6 +379,8 @@ public function setEncoding($encoding)
 
  /**
  * Get the current encoding which will be used on the POST data
+ *
+ * @return int a Request::ENCODING_* constant
  */
  public function getEncoding()
  {