Correct paths for utop-history, utoprc: in utop subdirs of XDG base dirs
Issue #481 described failure to load utoprc from its stated location PR #475 misidentified the issue as an incorrect README
In fact the paths were pointing to files within the XDG base directories themselves rather than in a subdirectory for the utop application.
This patch simply changes $XDG_STATE_HOME/utop-history to $XDG_STATE_HOME/utop/utop-history and $XDG_CONFIG_HOME/utoprc to $XDG_CONFIG_HOME/utop/utoprc
Added check & creation of history file's parent directory, fixing #478
This was exacerbated with the first patch because XDG_STATE_HOME/utop was extremely unlikely to exist on any system
I believe this should be the proper place since init.ml is also in .config/utop, and it's already documented like that in the README.
I also agree that this is more standard location. I am planning to merge if there are no objections.