Update to 3.42

Upstream changes:
3.42 - 2018-04-21

    * Include 'Changes' (this file) in the distribution.

3.41 - 2018-04-21

    * Fix security problem: CWE-134: Use of Externally-Controlled Format String.
    * Fix WIDEST_UTYPE.
    * Add the following functions:
      croak_sv, die_sv, mess_sv, warn_sv, mess, vmess, warn_nocontext,
      croak_nocontext, croak_no_modify, croak_memory_wrap, croak_xs_usage.
    * Delist functions listed as deprecated or unstable.
    * (perl #132876) define API macros on if the NEED_ macro is defined.
    * (perl #132876) only define croak_xs_usage()'s assert macro if cxu requested.
    * (perl #132761) updates for older perls.
    * Do not define PERL_MAGIC_qr more times.
    * Do not mask Perl_warn_nocontext and Perl_croak_nocontext.
      (Fixes compile errors on older threaded Perl versions.)
    * Skip ASCII tests on non-ASCII platforms.
    * Skip tests invalid on EBCDIC.
    * Will now compile under C++11.
    * Documentation improvements.

(wen)