Add Nuncabola UFO ball.
Merge pull request #80 from Cheeseness/nuncabola-ufo

Add Nuncabola UFO ball.
Add UFO ball

Added UFO ball. Minor tweaks to ball list.
Add UFO and Catseye balls.

Added UFO and Catseye balls.
Update all level shots
Add release notes excerpt to README.md
* Renames current release notes document to release-notes.md to be copied to release-notes-1.6.0.md when no longer current
* Adds link to doc/release-notes.md to README.md
* Adds highlights excerpt from release-notes.md to README.md
Update help shots
Add paxed's gradients
Replace gui/demo2.nbr

Without disrespect to the original replay, this one is more accurate
and less wobbly.
Merge pull request #82 from Cheeseness/release-notes-fixes

Add release notes excerpt to README.md
Remove duplicate highlights section

Otherwise they're bound to get out of sync.
PO update
Update Greek language file
Fix hardcoded Neverputt fall-out height
Merge pull request #83 from ChallengeSY/paxed-grads

Add paxed's gradients
New PNG optimization pass

This commit optimizes PNG image files that were added or modified since
the last pass. In particular, it removes the alpha channel from several
opaque images (including all of paxed's gradients).
Update release notes