A not-so-recent update to projectile caused doom-project-root's
signature to change (it can now return nil, if not in a project). This
fixes +neotree/open and +neotree/find-this-file to account for this new
behavior, by resorting to default-directory in the absence of a project.
projectile-project-root no longer returns `default-directory` if not in
a project (it returns nil). As such, doom-project-* functions (and their
uses) have been refactored.
+ doom-project-p & doom-project-root are aliases for
projectile-project-p & projectile-project-root.
+ doom-project-{p,root,name,expand} now has a DIR argument (for
consistency, since projectile-project-name and
projectile-project-expand do not).
+ The nocache parameter is no longer necessary, as projectile's caching
behavior is now more sane.
+ Removed some projectile advice/hacks that are no longer necessary.
+ Updated unit tests
