Improving the `buffer` module

[m4rw3r]

Rename module to stream, since it provides tools to deal with streaming data, not just buffering.

Renames

• stream::Source <- data_source::DataSource
• stream::IteratorSource <- data_source::IteratorDataSource
• stream::ReadSource <- data_source::ReadDataSource
• stream::FixedSizeBuffer
• stream::GrowingBuffer
• stream::BufferedInput <- InputBuf
• stream::Slice <- SliceStream
• stream::BufferedSource <- Source
• stream::Error <- StreamError
• stream::Buffer
• stream::Stream

  Fixes/Updates

• Source::read should either be unsafe or should always be provided with zeroed memory.
• Error only use Retry where the stream itself will attempt to refill before trying the parser again, and Incomplete should be used otherwise if the parser requires more data.
• Look at how Tokio manages buffers and see if we can get that to mesh with Chomp