Bump version to 4.3.0

update release version to rc4 in configuration

Merge pull request obgm#668 from mrdeep1/truncation

examples: Fix truncated usage() output

pdu.[hc]: make token argument const in coap_pdu_duplicate()

configure.ac: bounce version number to v4.3.0rc1

Set library version to

LT_LIBCOAP_CURRENT=3
LT_LIBCOAP_REVISION=0
LT_LIBCOAP_AGE=0

Release 4.2.1

configure.ac: bumped version number to 4.2.0

Release candidate 4 for version 4.2.0

Release candidate 3 for version 4.2.0

Release candidate 2 for version 4.2.0