Added module reloading API and CLI interface

[calebstewart]

Description of Changes

This PR adds the ability to reload pwncat modules at runtime. This is facilitated through the addition of a new flag for the Manager.load_modules method, which now takes a force keyword argument, which forces reloading of previously loaded modules. Further, there is now a new Manager.reload_module method which accepts either a module instance or a module name to be reloaded specifically. Both load_modules and reload_module methods will also attempt to fix the current module context if a module is being reloaded, and reset any module configurations, which could fail if the module arguments have changed during reload. If a module-specific configuration fails to apply after reloading the module (likely because the module arguments changed on disk), a warning is printed and that configuration is lost.

Lastly, this PR adds new arguments to two pwncat commands: load and run. First, the load command now as either --force/-f or --reload/-r arguments. These are synonyms which force a reload of modules during loading (through the force argument of Manager.load_modules). Second, the run command now accepts a --reload/-r argument which forces the selected module to be reloaded via Manager.reload_module prior to execution, which should be useful when debugging a new module (or a misbehaving old module).

Fixes #241.

Please note any noqa: comments needed to appease flake8.

Major Changes Implemented:

• Added force argument to Manager.load_modules to enable reloading modules.
• Added the Manager.reload_module method to reload a specific module.
• Added --force/-f and --reload/-r arguments to the load command (#241).
• Added the --reload/-r argument to the run command to reload modules prior to executing.

Pre-Merge Tasks

• Formatted all modified files w/ python-black
• Sorted imports for modified files w/ isort
• Ran flake8 on repo, and fixed any new problems w/ modified files
• Ran pytest test cases
• Added brief summary of updates to CHANGELOG (under [Unreleased])

For issues with pre-merge tasks, see CONTRIBUTING.md