Add $MASK and $MASKFILE_DIR utility env variables

[jacobdeichert]

Describe the problem

When referring to a maskfile with --maskfile <path_to_maskfile>, scripts inside can't simply use mask <command> to call other subcommands since mask tries to look for a maskfile in the current directory you're calling from. The new instance of mask can't understand you called an external maskfile that's not within this directory.

Describe the solution

The solution to this is a utility environment variable, $MASK. Instead of your scripts calling mask <command>, to make them location-agnostic, you should use $MASK <command> instead. $MASK is just equal to mask --maskfile <path_to_maskfile> which means you no longer have to worry about where you call a maskfile from.

Another utility variable was also added: $MASKFILE_DIR. This allows us to refer to the directory the maskfile lives in which can be handy for loading relative files to it.

How to test

Use $MASK within a script to call another subcommand.

• Added unit tests
• Added integration tests

Types of changes

• Bug fix
• New feature
• Breaking change