feature request: automatically enter environment when cd-ing into dir

[gzur]

What is needed here is a way to mark directories as haz-devenv.

Proposed solution is to introduce a dotfile/dotdir á la git.
The existance of a .devenv file/dir in any directory would trigger the automatic invocation of the relevant environment.

This .dotfile/.dotdir could be used to store other configuration (like base_image, default_interpreter, and other such stuff)

[gzur]

the solution to this would affect the solution to #3 and vice versa