feat: handle breaking changes

[BlueNc]

Hello,

I add the support for breaking change commit, according to Conventional Commits.

Exemple:

With theses commit messages :

feat!: description1
----------------------------------------------------------------------
feat(scope): description2

BREAKING CHANGE: breaking_change_details

generated markdown :

# Title

Description

## Unreleased (2020-01-01)

#### New Features

* description1
* (scope): description2

#### BREAKING CHANGES

* description1
* (scope): breaking_change_details

Tests :heavy_check_mark: Formatting using Black :heavy_check_mark:

[Michael-F-Bryan]

@BlueNc the current maintainer for this library is @KeNaCo.

[KeNaCo]

Hi, thank you for your PR. I apologize for the late answer, I will try to take a look at the weekend.

[KeNaCo]

Hi guys, sorry for not moving things as fast as I wish, I had no free time past two weeks(work, ill child..) hopefully I will be able to go thru all PMs this weekend.

[chris-noverde]

Any news?

[gsemet]

can someone take over this ?