Feature request: create directory specified by 'guppy lpca --out-dir' if it doesn't already exist

[nhoffman]

Not a big deal, but now it causes an error - I'd have expected it to just make the directory.

% guppy --version
v1.1.alpha14-96-g0d3d3e7
% guppy lpca output/redup.jplace.gz:output/specimen_map.csv -c ../cf_refset/cf.named.1.1.infernal1.1.refpkg --out-dir lpca --prefix cf.named.1.1
Uncaught exception: Sys_error("lpca/cf.named.1.1.xml: No such file or directory")
Fatal error: exception Sys_error("lpca/cf.named.1.1.xml: No such file or directory")