Replace HEXFILE rule by a rule for each type.
HACK: Adding '-Oformat' after OFLAGS overwrite the value in flags.

OBJCOPY was called without arguments so only copied the elffile in a file named
.hex.
Cannot build an '.hex' file for mips-malta so use a .bin output.

 Makefile.include: separate `link` in subtargets

tests: enable ps_schedstatistics and struct_tm_utility on-hardware CI tests

doc: remove sys_util references

* Add ELFFILE, HEXFILE, print-size targets

$(BINDIR)/$(APPLICATION_MODULE).a target builds libraries in RIOT and in DIRS.

Uses a FORCE phony target dependency to force rebuilding but still let
`make` use the file modification timestamps

Refactor osx-native linker rule into `_LINK` too.

sys/include/xtimer: Added xtimer_set64()

xtimer: Add XTIMER_SHIFT = 6 automatic option

examples: rename MQTT-SN example for clarity

net: added CoAP RD client for simple node registration

cpu/atmega_common: use __temp_reg__

pkg/ccn-lite:enable CS dump in shell command

tests/periph_flashpage: fix typo in doxygen header

boards/nucleo-l433rc: initial support

gcoap: return Method Not Allowed if appropriate

boards: slwstk6000b: add support

tests: adjust MAC test folders' names.

netopt: move NETOPT_BLE_CTX to new netopt doc style

Documentation of the option types was clarified in #8655. I only noticed
after merging #8884, that `NETOPT_BLE_CTX` was not documented using
that new style. So I deliver the change myself to make it quicker.

net: add Skald, a BLE advertising stack

Skald is a very small and simple, TX-only BLE stack that supports
sending advertisements only. It is useful for building all kinds
of BLE beacons with very minimal memory footprints.

examples/ccn-lite-relay: use xorshift PRNG