Minimal support for execution of a parsed program

[jberthold]

Given a pretty minimal true.rs:

fn test_true() -> bool {
  true
}

What needs to be done?

• User calls koat true.rs from CLI
• The stable MIR json gets generated from the source file
• The needed information (blue graph?) from the JSON is loaded into the initial K configuration
• A claim with the proper requires/ensures clauses gets generated from the config
• The claim gets symbolically executed
• Relevant information from the execution result is gathered and reported to the user

[gtrepta]

Before we do the test_true function, it would be a good idea to implement functionality for test_unit() -> () to work out control flow first, before handling data.