Released v3.0.0

• Fixed: (BUG): packed cxc_stack members were not correctly aligned for WORDSIZE==64
• Fixed: new version of m4/build_switch.m4 - the previous version was incomplete and buggy.
• Change: cxc_backtrace(), cxc_backtrace_buf(): in case of error the error message is printed to defined fd/buffer (if possible)
• Added: new public function: cxc_get_sig_desc(): fully safe replacement for strsignal(), used in cxc_backtrce().
  The most important change hoowever, is upgrade to returncode v1.0.2. This version significantly increases functionality of the rcode, but requires special pre-build steps, which are performed using bash script: 'rcd_autogen'.
  Additionally, the m4/rcd_autoconf.m4 script is provided, to ease integration of 'rcd_autogen' with autoconf.
  The new rcode allowed to implement 3 new public macros:
  CXC_TRY_MSG(), CXC_MARK_MSG() and CXC_THROW_MSG().
  Now it's possible to connect rcode values with corresponding textual messages or comments, which are visible in the backtrace.
  Manpage and test program are updated.
  Besides that, lots of small changes and fixes have been introduced, see change log for details.