add map merge functionality

[shovelwagon]

Proposed code for enhancement in #1499.

[hashicorp-cla]

All committers have signed the CLA.

[shovelwagon]

@eikenb, I was wondering if I could get a review. We're looking to move pretty quick with this new functionality.

[lornasong]

Hi @shovelwagon, thanks for the PR! @eikenb is currently unavailable but will be around to review next week. I left a couple comments for minor nits that I noticed from an initial look but will leave it up to @eikenb!

[shovelwagon]

@lornasong, thanks for the initial review!

[shovelwagon]

@eikenb, just wondering if there's anything you need from me? We're looking to get consul-template in our build pipeline within the next week and ideally we're not running on the fork.

[eikenb]

Hey @shovelwagon,

I was going to wait until after I got 0.27 out to look at this but as it is a template function, so self contained, I'll take a look at it tomorrow while I'm waiting on some feedback on another PR (for 0.27).

[shovelwagon]

Thanks @eikenb!