v2.0.0 Beta 2

• Added HttpRequest and HttpResponse as abstract base classes for requests and responses. HttpRequest includes methods for getting and setting query parameters
• Moved Rfc7230 to Http1 sub-namespace.
• Renamed header methods using the term "raw" to use "pairs" instead, e.g., getRawHeaders() → getHeaderPairs(), parseRawHeaders() → parseHeaderPairs()
• Added convertHeaderPairsToMap() function to convert header pairs returned from functions such as Rfc7230::parseHeaderPairs() into a map similar to that returned by Rfc7230::parseHeaders().
• Passing an int, float, or Stringable as an array value to HttpMessage::setHeaders() will cast the value to a string instead of throwing a TypeError.