Add a link on title to compare changes between two releases

[khiav223577]

For example:

v1.1.6 2017/07/30

• xxxxxx
• xxxxxx

Add a link on v1.1.6 to compare changes between v1.1.5...v1.1.6

v1.1.6 2017/07/30

• xxxxxx
• xxxxxx

[lalitkapoor]

@khiav223577 If you're up for it, I would be happy to review a PR for this.

[khiav223577]

I open a PR for this :)
It seems like there is no test case, so I only test it on my repositories.