feature: dynamic environment variable injection for blog

[ttimochan]

I would like the blog program to allow for dynamic injection of environment variables after the build is completed, rather than requiring a rebuild every time an environment variable is changed.

[eeg1412]

I would like the blog program to allow for dynamic injection of environment variables after the build is completed, rather than requiring a rebuild every time an environment variable is changed.

This is one of the main reasons I've been reluctant to use Docker; there's no way to dynamically inject environment variables.