Create dependency output directory recursively when copying

[gadenbuie]

This PR fixes #331 by having copyDependencyToDir() create the outputDir recursively. Previously, this was a side effect of a later call to file.copy(), so this change makes the recursive directory creation explicit. It's also necessary when a nested directory is required because normalizePath() will fail otherwise.

[gadenbuie]

cc @cpsievert @schloerke since I can't request reviewers in this repo.

[cpsievert]

Thank you!