Adopt Semantic versioning for releases

[Simon Le Bourdais-Cabana]

Introduction

We've been using tflint for a while now and has been a smooth ride up to now. For different reasons, the tflint version was pinned to an older version. We also have a custom rules plugin. When we updated dependencies of the plugin, the api used was bumped but the tflint executable that uses it was not... and then everything broke even though no major major versions of tflint had been released. With that said, a minor release of tflint could have exposed a new api while being backward compatible. Although, the SDK did not get its major version upgraded as well when removing support for older tflint versions. Going through the releases, there are notes of breaking changes here and there, pretty well documented.

Proposal

Adopt semantic versioning for releases version of tflint and its plugin sdk in order to better communicate impact of new releases.