Adds the ability to load alternative fig files, and to specify and load environments. 

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