If the attribute name is passed, then it is the one used to process the option
--target[s] of waf build. The board name should be used only in configuration
time. The build targets should be board/platform agnostic.
Now, instead of using `waf --target ArduCopter.sitl`, we use `waf --target
ArduCopter` and the binary continues named as "ArduCopter.sitl".
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.
It was implemented in such a way that gtest is required only if the user wants
to build and run tests. Initially we're considering all tests should be gtests.
We can change that assumption in the future if necessary.
We're currently using the tests standard error for reporting tests. We can add
TAP later to integrate with other tools.
Additionally, this patch simplifies the exclude patterns passed to
collect_dirs_to_recurse.