Show the full commit message as tooltip #880

Description

I need to see the full message of a commit as a tooltip. Currently, the package only shows the message headline as a tooltip, which isn't very useful (at least for me)

Steps to Reproduce

1. Open Atom
2. Open a PR (e.g this one)
3. Scroll down to a commit that has message body (e.g this or this)
4. Hover on that commit

Expected behavior:

A tooltip with full commit message (not just headline)

Actual behavior:

A tooltip contains only the commit message headline

Reproduces how often:

100%

Versions

# atom --version
Atom    : 1.18.0-beta0
Electron: 1.3.15
Chrome  : 52.0.2743.82
Node    : 6.5.0

# apm --version 
apm  1.18.1
npm  3.10.10
node 6.9.5 x64
python 2.7.12
git 2.7.4

Additional Information

Proposed solution

We can retrieve message attribute instead messageHeadline then set it as tooltip (AFAIK, messageHeadline has no other usage)

I can open a PR for it in case this solution makes sense