Basic parsing expression library

[kwvanderlinde]

Overview

We need a basic implementation of parsing expressions.

Acceptance Criteria

• A fully functional parser may be built from simple parsing expression objects.
• The parsing expression objects must implement a minimal interface with minimal dependencies and must perform no other actions other than parsing.
• The parser must implement a minimal interface with minimal dependencies.
• The design must be extensible. In particular, in the future we will want to add memoization
• Memoization is not required.
• Performance is not a concern.
• No builder is required.