WarcReader/GunzipChannel to check ByteBuffer in constructor, #21

[sebastian-nagel]

• fix detection of gzip magic in WarcReader if buffer has byte order little endian
• throw IllegalArgumentException if buffer is read-only or is not backed by an array
• document that buffer must be in read state
• add unit tests for buffer byte order, read-only buffers and a pre-populated buffer

[ato]

Thanks!

[ato]

Released as 0.9.0. Should sync to maven central in a couple of hours.