Sometimes you want to set specific environment variables during build.
For example, on some systems nodejs needs some extra options to be able to run correctly on low memory systems.
To make sure this will be loaded and works on both scripts and Dockerfile, you can now create a `.build_env` file.
This `.build_env` file should contain all the variables (including an export command) you want to expose during build time.
The template file has a nodejs example.
Closes#183
Signed-off-by: BlackDex <black.dex@gmail.com>
