examples: dunnart version of the simple calculator from my 1986 thesis

Signed-off-by: Peter Williams <pwil3058@gmail.com>
parser: remove ddlib/parser.d as it is superceded by ddlib/templates.d

Signed-off-by: Peter Williams <pwil3058@gmail.com>
symbols: move some declarations from ddlib/components.d to symbols.d as
they are not required by the generated parsers.

Signed-off-by: Peter Williams <pwil3058@gmail.com>