Warn on uninitialized variables

[coolhill]

Creating a new rule

• [x] Documented the code.
• [x] Added tests for the new rule in the amarna/tests/ folder.
• [x] Added the new rule description to the README file.

Pull request description

• Added a rule to warn on uninitialized variables ie local variables that are not declared to an expression and subsequently never referenced.
• For now also ignores if the variable appear in a hint or a part of the assert equal instruction(inst_assert_eq).