* README.md: Now backward-compatible back to Ruby 1.9.2
* lib/clamav/responses.rb : Change insufficient comparison
* lib/clamav/commands/instream_command: Support of INSTREAM

This commit brings support for the INSTREAM command, that allows
scanning viruses inside raw data streams.

Some changes have been made to the public API of the `Connection`
class that requires to update the major version of the gem.