Remove a semi-colon
Replace all String#[0] with String#bytes#first

In Ruby 1.8, hi[0] returns h has a byte.
http://ruby-doc.org/core-1.8.7/String.html\#method-i-5B-5D

In Ruby 1.9 and 2.x, #[] returns a slience
http://www.ruby-doc.org/core-2.1.1/String.html\#method-i-5B-5D

All versions respond to #bytes, so this change respresents a
backwards compatible change and bugfix on newer Rubies

closes #5
Use floats for Originate Timestamp and remove unused variable
Use IO.select and immediately set the client receive timestamp

I found this to give a more accurate timestamp because the stamp is set
immediately upon the wakeup that data is available, rather than after
the data has been transfered to userspace.

As a result, the timestamp is now passed into the Response object when
it is constructed.

closes #6
Add Response#offset and the start of a test that validates it

The test is quite hard if your clock is in sync. I'm not sure the right
way to actually do this because we're using a pool of NTP servers and
ntpdate and Net::NTP could hit different servers.

I think this is good enough for now to verify that things actually
work and return reasonable results.

closes #6
Merge pull request #7 from marcbowes/master

Fix for 1.9, expose Response#offset. Fixes #5 and fixes #6.