Implement -b option to specify branch in Readium

[pablotoledo]

I propose adding a new option -b or --branch to the command line interface of readium. This option should accept the name of the Git branch as an argument. The tool should then clone and process only the specified branch instead of the default branch.

Here is an example usage:

readium https://github.com/username/repository -b feature-branch

[pablotoledo]

Created a new branch feat/branch for this issue