Correction of the documentation

Change-Id: I2f0d4c9774e5afe5e29a517fa92bd04b358b5b3c
Checks the external ALRM signal handler

- Test t/??_io.t checks the external ALRM signal handler.
- Minor improvements in documentation.
- Changes to the Changes.

Change-Id: I2f43863e48e5e7ea33999444fbd81d95ab062140
Improve timeouts handling

refs #67
CHANGES:
    - You can disable ALARMS usage by Kafka by passing timeout => undef to
      Kafka::Connection->new or Kafka::IO->new. In this case '$REQUEST_TIMEOUT'
      is used for the most of IO operations.
    BUGFIXES:
    - Kafka::IO->new preserves external alarms but this may delay alarm signal
      delivery (thanks to Stephen Sprague).

Change-Id: Ic923c43d953870f6a77c515e31143f6919b3fc21