Upgrade --save

[JamesMcClung]

Upgrade --save. It now:

• Can take an arbitrary string to set dir, name, or format. Format/ext is greedily parsed first (substring after the last .), then the name/stem, then the dir.
• Can specify individual components more clearly with dir=<dir>, name=<name>, and format=<format>.

Remove --save-format.

Note that this is a breaking change: -s dir (literally "dir") will now create dir.png/dir.mp4 in the current working directory instead of dir/<autogenerated stem>.<ext>. To achieve the previous behavior, append a / to the end of directories, e.g. -s dir/, or use -s dir=dir.

Here's a helpful diagram of behavior:

-s arguments	dir	stem	ext
(none)	–	–	–
out/	out	–	–
fig	–	fig	–
.gif	–	–	gif
fig.gif	–	fig	gif
out/.gif	out	–	gif
out/fig.gif	out	fig	gif
.	.	–	–
./..	./..	–	–
dir=out name=fig format=gif	out	fig	gif
name=fig.i	–	fig.i	–

Note that the default dir is ., default name is automatically generated, and default format is determined by the plot type.