• Added constructor to read_input<> that accepts a FILE*, see issue #78.
• Enhanced apply<>, apply0<> and if_apply<> to support apply()/apply0()-methods returning boolean values.
• Simplified implementation of raw_string, the optional Contents... rules' apply()/apply0()-methods are now called with the original states.
• Fixed the tracer to work with apply()/apply0()-methods returning boolean values. (Thanks Joel Frederico)
• Fixed, simplified and improved examples/parse_tree.cpp.