Replace instances of 'hash' with 'object' in documentation

Context: https://twitter.com/mvirkkunen/status/506796515982311424

Many of us programmers know what "hashes" are in the general sense, but the word is not part of the JavaScript vernacular and could be unfamiliar to newcomers. This PR replaces instances of "hash" with "object" in various markdown documents.

"Directories object" is less clear than hash. What is this thing? How is it intended to be used by CommonJS? "hash" captures the spirit of what it's doing at the OS / shell level in a way that object does not.