more granular development instructions

[dmitris]

I believe the current development instructions https://github.com/yahoo/athenz/blob/master/docs/dev_environment.md are too "monolith" - they tell you to run mvn install. Would it be possible to break them into more granular pieces - for example, if someone wants to do development on the Go client pieces, what they need and whether it is possible to avoid dealing with the whole Java "bulk"?

[dfsutherland]

Also: Should I expect to be able to build according to the development instructions on a Mac? Or should I expect success only on a Linux box of some kind?