Add inner commits analysis for squashed commit

[GuiBL4]

This PR aims to create a new feature for repositories using a squash-and-merge strategy for the commits.

This feature uses the GitHub API to retrieve the inner commits inside a PR that has been squashed-and-merged. Each inner commit contains the conventional message <type>(<scope>): <subject> that has to be analyzed by the semantic-release process.
Thus, the message of the squashed-and-merged PR must follow a guideline and finish by a (#[number]) like :
Some-issue-to-solve (#3)

Here's the structure of a PR with a squash-and-merge strategy :

The number inside parenthesis refers to the PR's number used by octokit.request to get the inner commits.

We provide some tests. However, as octokit needs a repository to get the PR, a specific one was created and documented for these tests. This test repository is here.

An option has been added with a flag -s or --squashMerge to use this strategy.

[travi]

as highlighted in our documentation, we recommend avoiding squash when you are making multiple changes like you mention. when your commits are atomic, this type of functionality is unnecessary. we appreciate your effort with this contribution, but please confirm with maintainers that there is interest in the change to save yourself from wasted effort.

in this case, we are not intending to support multiple changes in squashed commits.

[GuiBL4]

No problem, we developed this feature for our internal use. However, we will run our fork to be able to use it. Have a nice day.