0.12.0

IMPROVEMENTS:

• Add parsley.NonTerminalNode interface for nonterminal nodes
• Add parsley.StaticChecker and parsley.StaticCheckable interface for doing static analysis
• Add type to the AST nodes

BACKWARDS INCOMPATIBILITIES:

• The parsley.Interpreter's Eval now expects a parsley.NonTerminalNode instead of a list of nodes
• The ast.NodeList's node methods will run always on the first node only
• The ast.NilNode was renamed to ast.EmptyNode to avoid confusion
• The ast.NewTerminalNode now expects a new valueType parameter
• Most of the text/terminal parsers now will return a custom node type (string node, int node, etc.)