add - env variable expand
mod - cleaner standard way to expand env variables
Merge branch 'feature/interface_bind' into develop

add - interface binding to the port forwarding

Case like:

- 172.17.42.1:4245
- 172.17.42.1:4246:4246
- 172.17.42.1:4247/udp
- 172.17.42.1:4258:4248/udp

are now working
Merge branch 'feature/env' into develop

add - environment variable expansion in the fig.yml file
mod - interface binding function didn't work if no ports were specified
mod - fix no ports case in fig/service.py:__port_binding