Store more metadata

[jamadden]

• RelStorage cache size and history status (maybe the entire relstorage options dict?)

I've wished for those when I forgot to include them in the file name for the output.

Also, this should be its own issue, but it would be nice to have the ability to automatically create filenames/directory trees. And we should always save a file, even if it's just temporary, because sometimes you don't realize you wanted to compare the results until after you ran.