global: silent version from git

* Silences the warning "fatal: Not a git repository ..." when running
  inveniomanage outside of a git repository.

Signed-off-by: Jan Aage Lavik <jan.age.lavik@cern.ch>
docs: jsonalchemy grammar and rewording

* Rewords sentences that were incomprehensible or hard to understand
  and splits long chunks of information into bullet points.

* Changes informal pronouns to formal.

* Fixes a triple-quote.

Signed-off-by: Dimitrios Semitsoglou-Tsiapos <dsemitso@cern.ch>
installation: addition of MacOS installation guide

* Addition of a section on how to install invenio software
  on MacOS 10.9 or later.

Signed-off-by: Konstantinos Kostis <konstantinos.kostis@cern.ch>