Add Tags and change summary

[danielewood]

This PR adds a change summary with colored highlights.

Also adds my bash function to allow use in pipelines and full support of all standard tool flags.

For example, you can run tfsum --target=example

Resolves #4

[containerscrew]

Hey @danielewood thanks again for your PR 😀 Let me try this feature. Just what I wanted to implement, verbosity in output changes. FYI, tftools it's also available in my custom infratools image. https://github.com/containerscrew/infratools (I will push a new tag when I merge this MR).