Custom Environments / Cache Keys

[charlespierce]

Currently, we have a single global cache for all of the tools. However, some corporate environments have a limited subset of versions available (e.g. only specific versions of Node are available for internal use). For users who work on both internal and external applications, it would be nice to have some way to specify that internal tools use a separate cache from external tools, that way there's no chance of accidentally polluting the internal project with a version of Node that isn't actually available.

Similarly, it would be useful to be able to specify a hooks.json file that applies to multiple projects, but not all of them, through some sort of "Environment" value, so that users who work on multiple internal and external projects can point to an internal repository without having to customize each internal project individually with a full hooks configuration.