Find all libraries required by a given package

[jackmaney]

• Use ast on all of the .py files and get a list of imported modules.
• From this list, remove modules that are:
  • Built-in to Python (via stdlib_list), or
  • In the given package itself (might be tricky...).
• Use pkg_resources.require on any remaining modules in the list to see which are installed (see this useful Stack Overflow answer).
• Return a report listing (if found):
  • Modules that are imported but not found.
  • Modules that were listed as requirements, but not actually imported.