Move treematch support to v3.x

[jsquyres]

This is a ticket to ensure that we don't forget to move treematch over to v2.x when it has soaked on master long enough.

[jsquyres]

@bosilca Looks like this was addressed in #725 -- is treematch complete on v2.0.0 / should we close this issue?

[bosilca]

No, nothing has been moved into the 2.x yet. I assign this issue to me, so that I can keep track of it.

[hppritcha]

should the milestone for this issue be moved to v2.x?

[jsquyres]

at this point, I think so.

[bosilca]

I can create the PR now, but I was waiting for a decent period of time with this on master before.

[jsquyres]

Your call. If you think it's ready for v2.0.0, cool. If you want to wait until v2.1.0, that's fine too.

[bosilca]

it is gaining traction, I would rather prefer to have it in the official release, so that people will get access to it by default.