declare the inline function opt_finished static

an `inline int opt_finished` causes GCC to spew this error when used
with -std=gnu99:

libcoap/option.c:165: undefined reference to `opt_finished'

Signed-off-by: Olaf Bergmann <bergmann@tzi.org>
option codes updated according to coap-18
Basic list wrapper to align utlist.h with Contiki's list API.

This file was originally part of tinydtls.
(cherry picked from commit 5db598c45533b5471bb8c8bd6fac8f67b62df80d)
added missing t_list.h to HEADERS
notifications and observer removal according to draft-ietf-core-observe-09
bugfix: set new random value when more than sizeof(v) bytes are requested

The function contiki_prng_impl() used to fill the entire buffer with the
same two bytes of random data. (Thanks to Andreas Bender for pointing out.)
option number for Accept has changed in coap-18, fixed test_encode_pdu5()
added new test cases for error response generation

test t_error_response8 will fail when COAP_MAX_OPT < 2000
increased size of argument type to support large option numbers

Note that the bit field for filters would grow very large if
COAP_MAX_OPT is set to larger values.
bugfix: #17 coap_opt_size underestimates space usage

Fixed calculation of option size in coap_new_error_response(). As
only some options are copied from the request, the delta value can
increase and thus require more space to encode. This fix closes
https://sourceforge.net/p/libcoap/bugs/17/ (thanks to chrysn and
tbahls for pointing this out).
updated ChangeLog and increased patch level
Merge branch 'master' of ssh://git.code.sf.net/p/libcoap/code
Fixed output of IPv6 addresses with Contiki in coap_print_addr()

Addresses have been truncated and possibly had the wrong byte order. Thanks
to Andreas Bender for pointing this out.
Merge branch 'master' of ssh://git.code.sf.net/p/libcoap/code
bugfix: off-by-one error in coap_print_addr()

The closing ']' was misplaced, and the pointer not updated correctly. Thanks
to Andreas Bender for pointing this out.
Add RIOT Makefile