New command: show

Initial implementation for command to select, parse, and show recipe data.
This initial implementation does not actually parsen and show the recipe
data.

Signed-off-by: Esben Haabendal <esben@haabendal.dk>
Very basic parser and show command

This initial parser implementation is only able to handle simple
assignment statements.  There is no rich variable model implementation, no
error handling, and no a-lot-of-things.  It is really not much more than a
stub.

Signed-off-by: Esben Haabendal <esben@haabendal.dk>
WIP: Basic string variable support

Signed-off-by: Esben Haabendal <esben@haabendal.dk>
tests: Add test recipe for string parser

Signed-off-by: Esben Haabendal <esben@haabendal.dk>