This introduces rbinstall.state, which contains functions (primarily

get_system_info()) for determining state that will be used throughout

the installer process.
get_system_info() determines the operating system and architecture of

the target system. This primarily centers around Linux (though there's

some WIP for macOS with Homebrew).
For Linux, information on the current distro is retrieved and parsed,

and used to determine the default installer method (Yum, Apt, etc.), the

distro ID and families, version, and other identifying information.

These will later be used for package selection.
The beginnings of rbinstall.install_methods was also added, providing

an enum of install method constants that are needed in

get_system_info().
Unit tests are available for state.py methods. We use kgb, pytest,

and pytest-sugar (an extension that provides better output and

immediate failure information for pytest runs).

Unit tests pass.
Tested this along with the rest of the in-progress changes on a variety

of Linux distributions.