TODO:

- Print error when tmp directory can't be deleted (in instant-clean).
  Maybe add username to tmp dir name suffix?
  /tmp on cluster contains instant directories 
  of many users.

- Keep a most recently used list
  add a max cache size option to ~/.instant/intantrc
  clean up the oldest modules whenever we exceed this quota

- Add argument to provide a cache subfolder name.
  Then instant-clean can take an argument to clean only the "ffc" cache subfolder etc.

- Does instant handle full disk properly? (Does any software? Define properly!)

- Fix arguments not used in setup.py

- Use object files argument.

- Improve documentation

- Add tests for all variants of cache mechanisms available now

- Clean up imports, don't use import *
