- Clean the framework target dir (i.e., delete) before building the framework.
- Allow customization of several params through env variables that can be set in the post build script (rather than using the project name). The static header dir, e.g., does not match the default set in the script when creating a fresh library in Xcode 5.1. So, allow overriding it (e.g., to /usr/local/include which appears to be the default).
Merge pull request #1 from FitnessKeeper/customize-params-and-clean

Cleans the framework before building and allows customization of some params through env vars.