Ssh-session-manager

- **Note:** v0.2.0 has breaking changes
- The `SSHSessionManager` now spins up a separate thread for each `SSHSession`, a change needed to
fix the previous strange requirement of having to call a `print_command_output()` in order to keep
the `SSHSession` from exiting before the command finished. This function no longer exists,
blocking happens automatically, and printing out output is set via an input parameter to both
`run_commands_in_all_ssh_sessions()` and `run_command_in_ssh_session()`.
- `SSHSession`s now store standard output, standard error, and the command exit code
- `SSHSession` no longer provides the ability to capture specific output. Since all output is now
captured and saved, it is up to the user to search through it to find what they need.
- Removed some code, marked some items as "private" via `__`.
- Some functions have been renamed
- `SSHSession` no longer takes in a `session_description` variable in the `__init__()`

- **NOTE:** v0.1.0 has breaking changes
- Implemented a system to hold the output of all commands ran on a session. The `SSHSessionManager`
holds a dictionary that maps an `SSHSession` object to an internal dictionary. This internal
dictionary maps the `Command` object to the captured output message. Output is no longer stored
in the `Command` objects.
- The internal dictionary that holds the captured output, as mentioned above, will now also capture
the exit code for the command that ran as well. Execution is now blocked on both the captured
output and the exit code of the command, so that the session will not end until both of these are
captured (unless the user doesn't request any output to be captured, then execution blocking will
only happen on the exit code).
- Added print statements for some errors that were previously being omitted from output.

- Small documentation / repository changes

v.0.0.1

- Initial release