*) updateImage() now takes invalidated as a parameter
*) added example of how to dynamically generate images
Update backlog.md
Update backlog.md
Merge remote-tracking branch 'upstream/master'
Merge remote-tracking branch 'upstream/master'
Reject imagePromise before purging and make re-implement purgecache.

Rejecting imagepromise before the are discarded fixes issue #5. The
then() function is never called and the cacheSizeInBytes is not set into
an incoherent state.

purgecache was modified for clarity.
Merge pull request #8 from jpambrun/origin/fix/rejectBeforePurge

Fix #5 by rejecting imagepromise before the are discarded