Mostly non-functional change adding options to various features. In addition
to adding a JPEG option, add it to OPTIONS_DEFAULT. This is useful because
heif-convert is one of the few ways to convert a .heic photo to .jpeg, and both
are commonly used for similar media where .png does not necessarily make sense.
Correct the LICENSE for the examples code -- in 1.3.2, it is GPLv3+. (Though
in later git versions, they are relicensed to MIT.)