Usability Improvements

[divjotarora]

A few things I think could improve usability. All of these are based on monger version 0.10.0.

Behavioral Changes

• monger delete X.Y doesn't work. It requires specifying X.Y.Z. This is inconsistent with both monger start and monger run.
• monger delete <version> doesn't clear the corresponding data files in ~/.monger/db/<version>. I can see the case for wanting to keep the data files around, though, so I'm not too invested in this one.
• The format for running a binary using monger is monger run 4.4 mongo but when starting a cluster with phil, it's phil single 4.4. This is super minor, but the inconsistency in the version placement makes it a little less ergonomic to use.

New Features

• Download versions from a custom URL.
• Update a version given a URL. This is useful when working with latest variants, which get updated pretty frequently, but have a stable URL. This is definitely a nice use case, so I'd understand if you don't think it belongs in a general-purpose tool.

EDIT: I think the "update a version" can be done as monger get --force, so that doesn't seem necessary.