Make maximum window size configurable

• Avoid emitting compressed blocks when the compressed payload is not smaller
  than the raw block. (#105)
• Fix Dictionary decoding. It should not panic on invalid inputs.
• Make the decode window size limit configurable via FrameDecoder::set_max_window_size/max_window_size, StreamingDecoder::new_with_max_window_size, and the DEFAULT_MAX_WINDOW_SIZE constant. The default stays 100mb. (#111)
• Apply the window size limit to the first frame of a stream, not just later frames. (#111)
• Breaking FrameDecoderError::WindowSizeTooBig gained a max field and now reports the effective limit. (#111)