Refactoring and Bugfix

[patbec]

The following changes were made in the refactoring.

Minor changes:

• Documentation updated.
• Refactoring.

Major changes:

• Specified users are checked for their existence before execution.

Breaking changes:

• Variable zsh_users_config and zsh_system_config uses relative paths, it is no longer necessary to specify a full path.
  Naming of the property filepath has been changed to filename.

Bugfixes:

• Fixed incorrect resolved $HOME variable. The user path is now determined via the user module.

^{Changes included in changelog.yaml.}