Enable Pen to Manage Python Packages to Become a Package Manager

[Guibi1]

Adding these new features and commands:

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

What's missing:

• [x] Installing python if the required version is missing.
• [x] 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.