Instead of a dictionary of dictionaries, have a dictionary of
ConfigSets. Using ConfigSet have two benefits: (1) allow easily copying
values from other, (2) have syntax for specifying the keys directly as
attributes.
With this change now it's easier to specify minlure without
repetition. New boards can override a value, append or prepend depending
on the need.
DEFINES attribute is treated as a dictionary instead of a list, so
that's easier to override values (at expense of ordering). When reading
the board environment, the code converts back to a list.
The board configuration is now stored in a separate file, there's also a
function to get the boards names.
Caio Marcelo de Oliveira Filho