Please don't merge yet.

@jedgarpark brought up an issue with adafruit_imageload; its missing the bmp subfolder in the releases.

This PR doesn't fix it either, so I'll add it here.

Ok, reworked file selection when building the file list. It now includes package subfolders (adafruit_library/subfolder). Fixes previous comment, which was identified in Issue 5 on the ImageLoad repo.

A side effect of this change, is that example subfolders are also included, but not annotated with the library name. Currently only one repo has example subfolders: LSM303. This requires a much larger change, and falls in line with #28.
Visual Reference:

(.env) ~/Dev/cpy-build-tools/.bundles:$> unzip -l test-4.x-mpy-732c144.zip
Archive:  test-4.x-mpy-732c144.zip
{"build-tools-version": "devel"}
  Length      Date    Time    Name
---------  ---------- -----   ----
    12327  2019-05-06 10:39   test-4.x-mpy-732c144/VERSIONS.txt
#-> package subfolders:
      485  2019-05-06 10:39   test-4.x-mpy-732c144/lib/adafruit_imageload/__init__.mpy
      749  2019-05-06 10:39   test-4.x-mpy-732c144/lib/adafruit_imageload/bmp/__init__.mpy
      747  2019-05-06 10:39   test-4.x-mpy-732c144/lib/adafruit_imageload/bmp/indexed.mpy
 
      309  2019-05-06 10:39   test-4.x-mpy-732c144/examples/crickit_dc_motor_simpletest.py
#-> example subfolders:
      347  2019-05-06 10:39   test-4.x-mpy-732c144/examples/fast_accel/fast_accel.py
      328  2019-05-06 10:39   test-4.x-mpy-732c144/examples/fast_mag/fast_mag.py
      859  2019-05-06 10:39   test-4.x-mpy-732c144/examples/raw_and_cooked/raw_and_cooked.py

What triggers the creation of a new library bundle? I thought they might just be periodic but the dates aren't regular so it suggests there's perhaps a (rate limiited?) change based approach here?

Is there a way to manually request a new bundle release to pick up the effects of this (non-library) change?

Just seen a new bundle so please ignore the previous comment or thank-you for prodding it,