Remove STDIN.read call from zxing/server.rb

Was using STDIN.read to verify that a parent thread was still running.
This caused problems in Ruby scripts that require to read user input (i.e.
when requiring zxing from IRB). Replaced with a loop that checks
Thread.main's status every 0.5 seconds.

This bumps version to 0.3.1

Version 0.2.1

Update gemspec and gem version.

Version bump to 0.1.1

Version bump to 0.1.0