With alt fig file and envs

Added support for setting alternate fig files, and specifying environments from fig files 
via the command line. 

Example:
fig -f alt-fig.yml <COMMAND>
fig -f alt-fig.yml -e development alt-fig.yml -e dev <COMMAND>

Environments are declared in the fig file as such:
cat alt-fig.yml
environments:
  development:
    web:
      build: .
      links:
      - db
      ports:
      - 8000:80
    db:
      image: orchardup/portgresql
  production:
    web:
      build: .
      links:
      - db
     ports:
     - 80
   db:
     image: orchardup/postgresql