A couple small but important fixes for Azure

Two small commits to get static-expiry working on Azure.

- The first is related to Azure not populating process.env.PWD. This causes the app to crash once it hits require('static-expiry'). Stack trace attached in the commit message.
- The second is related to Windows systems using backslash ("\") as the path separator
character is instead of slash ("/"). This causes problems using every URL generation location (prefile, postfile, path) except for query.

I made sure the unit tests are passing with these changes as well as tested my Node.js app running on Windows Azure.