Enable Pen to Manage Python Packages to Become a Package Manager

[Guibi1]

Adding these new features and commands:

• Config file
• Package manager (see below)
• Venv creator (no longer relies on the python venv module)
• pen init: Creates a new pen project with a specific python version
• pen add: Adds a package to an existing project
• pen install: Generates or updates a virtual environment
• pen activate: Opens a shell in the virtual env

What's missing:

• Installing python if the required version is missing.
• Being able to install a package version other than latest. (will need to implement version ranges)
• Proper package version identification based on the python version, os and architecture.

[azomDev]

create_env.rs got delete (which got replace with pen_init.rs)
but delete_env.rs got delete and there appears to be no replacement for it

[azomDev]

I added a few comments. It's a start for now as I did not take a look at the new code yet and I passed over some portions of the modified code.