Feature/add support for custom env files

[mrpiatek]

Added a feature to use custom .env files.
It is done via phpspec configuration with testing_environment_file setting.
The testing_environment_file will override the testing_environment setting.

Purpose:

• You can have a dummy env file without any credentials commited to the repo and used for spec testing,
• You can specify a different database connection in that env file that, for example, uses SQLite in memory database.

If you have any suggestions please feel free to message me as I'm more than happy to improve this. Thanks.

[dmk1991]

This would be an awesome addition to the package. Have ran into a few issues where being able set set a new .env file for PhpSpec bootstrapping would be very useful.

[BenConstable]

Thanks @mrpiatek. Sorry for the delay in getting to this, I've started a new job and have had a busy couple of months. I'll try and give this a proper look this weekend.