D2 now uses bison parsing to parse its config file and has starter
files for SimpleParser. This check-in uses only generic JSON context
parsing (i.e. no D2 specific grammar).

Added new bison/flex parsing files:
    d2_lexer.ll
    d2_parser.yy
    parser_context.cc
    parser_context.h
    parser_context_decl.h

Added new generated files:
    d2_parser.cc
    d2_parser.h
    location.hh
    position.hh
    stack.hh

Added new SimpleParser related files:
    d2_simple_parser.cc
    d2_simple_parser.h

src/bin/d2/Makefile.am
    Added bison/flex related entries and rules

src/bin/d2/d2_controller.h
src/bin/d2/d2_controller.cc
    D2Controller::parseFile() - new method which overrides base class
    version and calls new bison parsing to parse JSON config file.