Log Message:
autoconf-archive: update to 2019.01.06

Change log:

* Noteworthy changes in release 2019.01.06 (2019-01-06) [stable]

  The Autoconf Archive now has its own organization on Github. Therefore, the
  mirror has moved to https://github.com/autoconf-archive/autoconf-archive. The
  old location, https://github.com/peti/autoconf-archive redirects there.

  The macro AX_CODE_COVERAGE was modified to use AX_ADD_AM_MACRO_STATIC,
  and thus unfortunately usage was changed.

* Noteworthy changes in release 2018.03.13 (2018-03-13) [stable]

  The macros AX_R_PACKAGE and AX_PROG_DATE have been added. Many other macros
  have received updates.

* Noteworthy changes in release 2017.09.28 (2017-09-28) [stable]

  The macros AX_PROG_HELP2MAN, AX_RECURSIVE_EVAL, AX_SUBDIRS_CONFIGURE,
  AX_ELISP, and AX_PROG_EMACS have been added.

  Various macros have received updates. Please check the ChangeLog file or the
  history of the git repository for further details.

* Noteworthy changes in release 2017.03.21 (2017-03-21) [stable]

  Obsolete macros AX_CXX_COMPILER_VENDOR, AX_GCC_LIBRARIES_DIR, AX_GCC_VERSION,
  and AX_HAVE_OPENGL have been removed from the archive.

  AX_DEFINE_SUB_PATH has been marked obsolete as suggested in
  https://github.com/peti/autoconf-archive/pull/97.