pkg/spiffs: implement statvfs and improve doc

unittests: fix failed assertion caused by priority_pktqueue

pkg: fix URL for tiny-asn1 package

sys/netif: include release of iovec in gnrc_netif_raw

sys/netif: add missig pkt release in gnrc_netif_raw

tests: fix tests/gnrc_netif for changes in #6895

shell/netif: extend set state option

tests: fix python style E305

tests: fix python style E402

E402 module level import not at top of file

tests: fix python style E502 issue

expected 2 blank lines after class or function definition, found 1

E502 the backslash is redundant between brackets

nanocoap: fix doxygen grouping

sys/timex: make NS_PER_US unsigned

github: add pull request and issue template files

gnrc_gomach: add sender ID number limit in beacon packet.

drivers/at86rf2xx: Fix set/get of NETOPT_AUTOACK

The doxygen group for the networking module is `net`, not `sys_net`.
By using `sys_net` nanocoap appears in the [module
root](https://doc.riot-os.org/modules.html) of the documentation.

cpu/sam0_common: fix assert in periph/flashpage

pkg: ccn-lite: adapt to v2

boards/b-l072z-lrwan1: make sx127x default netdev

sys/auto_init: add auto init implementation for sx127x radio devices

drivers/sx127x: improve netdev adaption

net/gcoap: Require interface for link local address in shell example