GitHub supports different types of issue templates for a while now.
The following types are supported:

* Bug report
  (living in `.github/ISSUE_TEMPLATE/bug_report.md`),
* Feature request
  (living in `.github/ISSUE_TEMPLATE/feature_request.md`), and
* Custom issue template
  (living in `.github/ISSUE_TEMPLATE/custom.md`)

Our current issue template is mostly a bug report template, so this
moves it to `.github/ISSUE_TEMPLATE/bug_report.md`.

gnrc_ipv6_nib: Add capability to handle and send RDNSS option

sock_util: add posix dependency

core/byteorder: fix naming for htobebufs/bebuftohs functions

`sock_util` includes the `arpa/inet.h` header so it has `posix` as a
dependency to include the `sys/posix/include` include path.

drivers/at: at out-of-band data support for at commands parser

tests: cpu_efm32_features: add test application

Add SRAM based PRNG seeder

tests/monocypher: Increase stack space

tools: add mosquitto.rsmb MQTT-SN broker

Improving TinyDTLS package and dtls-echo example

Due to all the changes, this is basically a new version for this
example. The main benefit is the use of sock_udp but also the client
side is now more robust and reliable.

The parameters required for the PSK and ECC (e.g. keys) modes are moved
to an unique header.

The integration of TinyDTLS for RIOT has been merged into the
development branch of the official repository.

It will be officially available on the master branch in the next
release of tinyDTLS.

Other minor updates:
- Support for the RIOT's memarray
- tinydtls/sha2 is removed from the compilation for giving priority
to RIOT's sha2 functions.

boards/stm32l476g-disco: initial basic support

Docs: add "allow time to ACK before dismissing review" to maintainer guidelines

Makefile.include: fix board/cpu inconsistent include order

stm32f103c8: fix Makefile.include INCLUDES definition

As should have been done in the initial commit. Stack space set to the
amount described in the doc

Include order for board and cpu was

1. cpu include
2. board include
3. board common includes
4. cpu common includes

Its now changed to:

1. board include
2. board common includes
3. cpu include
4. cpu common includes

Verifications:

There are no common headers names between boards and cpus.
Except native that has a 'periph_conf.h' in cpu instead of being in board.

tests/driver_pir: remove redundant/double configuration from Makefile

boards/stm32f429i-disc1: add initial support