By default the tool uses all sequences that appear in any of the image
sets. To make it easier to see just the changes between a smaller
set of images and a large one, this lets you limit the sequences
to just those in the first set being compared.
Formerly, we wrote the file paths as given on the command line, the
assumption being that the output file was in the cwd and the paths
to the directories would be correct.
However if we want to generate the output file somewhere other than
the cwd the generated image paths don't work. This takes the location
of the output file into account and either generates relative paths
if the files are under the output file directory, or absolute paths
otherwise.
This uses nototools to get unicode names. It relies on new
api in nototools.unicode_data to get data/names of proposed emoji
that are not currently approved and so not in the standard data
files.