cbc: add 'strerror' subcommand

This new subcommand returns the textual description of an error inputted
in either hex or decimal form. Very handy for quickly deciphering output
in logs.

Change-Id: I964e86964c36208c4f2f56e32efd0d9953821858
Reviewed-on: http://review.couchbase.org/43137
Tested-by: Mark Nunberg <mnunberg@haskalah.org>
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Remove debian/changelog and RPM %changelog

This will be generated at build time from RELEASE_NOTES.md, and
installed as /usr/share/doc/libcouchbase2-core/changelog.gz, as normal
debian packages do with their upstream log.

The same semantics apply for the RPM changelog as well.

Change-Id: Ibea18cd9a9518aa677f2018300326b990f5c7600
Reviewed-on: http://review.couchbase.org/43138
Tested-by: Mark Nunberg <mnunberg@haskalah.org>
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>