- hello world mini Autotools tutorial
  there's mainly 2 parts: 1st is to write "configure.ac" and 2nd write Makefile.am 
  $ autoscan
  $ mv configure.scan configure.ac
  $ aclocal                # Set up an m4 environment
  $ autoconf               # Generate configure from configure.ac
  $ autoheader
  $ touch NEWS README AUTHORS Changelog
  $ automake --add-missing # Generate Makefile.in from Makefile.am
  $ ./configure            # Generate Makefile from Makefile.in
  $ make distcheck         # Use Makefile to build and test a tarball to distribute
  $ make
  $ make install

  configure.ac
	AC_INIT([helloworld], [0.1], [kylek389@gmail.com])
	AM_INIT_AUTOMAKE
	AC_PROG_CC
	AC_CONFIG_FILES([Makefile])
	AC_OUTPUT

  Makefile.am
	AUTOMAKE_OPTIONS = foreign
	bin_PROGRAMS = helloworld
	helloworld_SOURCES = helloworld.c

- misc
  config.h  -- you can include "config.h" in your .c code and use constants defined in config.h to write portable code
  ifnames.  -- use this command to list what 'constants' have be used from config.h in *.c files of current project
  2 awesome tutorials:
  -> https://robots.thoughtbot.com/the-magic-behind-configure-make-make-install
  -> http://markuskimius.wikidot.com/programming:tut:autotools