sample: use `optparse` instead of `argparse`

No extra funtionality provided by newer package `argparse` is used.
We revert on using the older `optparse` and become compatible with
Python 2.6.
sample: add total_seconds() function

Since in Python2.6 there is no method timedelta.total_seconds() in
`datetime` module, we have to add a helper function to perform the same
task.
sample: update dependency note

After some small changes from previous commits, code now can be run
using even the Python 2.5 branch.
Merge pull request #4 from xakon/master

Update `sample` to run on Python 2.5