ATM as background process

[pvk-developer]

Now we are able to run ATM as a background process with:

• atm start (by default) starts 1 worker and the rest api.
• atm status shows the current status of the process (if its runing and if does so where the server is listening and how many workers are running).
• atm restart restarts the process to default values if no others are specified.
• atm stop stops the process.

Improved API readme and added it to the index docs. Update on Makefile for the docs.

Resolve #130