Generate uniq pidfile per config file

This feature allows multiple tarsnaps to run on the same hosts, using different configs.

New Feature: workingpath

Merge pull request #8 from terjekv/master

Added support for the "working directory" option to tar, -C.

Make python 2 an explicit requirement

Merge pull request #7 from danrue/readme_improvements

Readme improvements

v1.1: Merge pull request #3 from Alives/master

Using more human readable date/time formats

v1.0: Merge pull request #2 from dferris93/master

Minor change for compatibility with python 2.4