setup.py: setup_requires -> install_requires
Update version
Update durus version requirement
Add support for site-packages to SConstruct script
Update custom date fields when non-custom periods are chosen

refs #7
Use git tags for version
Merge remote-tracking branch 'SPlyer/master'

* SPlyer/master:
  Use git tags for version
  Update custom date fields when non-custom periods are chosen
  Add support for site-packages to SConstruct script
  Update durus version requirement
  Update version
  setup.py: setup_requires -> install_requires