build: add very simple configure.ac
add a small wrapper around PKG_HAVE_DEFINE_WITH_MODULES

this automagically adds CFLAGS/LIBS to keep code DRY..
configure.ac: properly store configuration flags in config.h
mp-pkg.m4: increase readability
add file to gitignore
regenerate config.h.in
remove fix-config
DEFINES: resamplers config_ -> have_
conditionally compile timer and getch2
compile timers based on actual compiler checks

this should be a little more portable than checking for known platforms
don't try hard, just port over the configure checks!
mp-pkg: use AX_ prefix
configure.ac: remove debug info

this is available in config.log anyway!
check for avresample_set_channel_mapping
create macro to perform statement checks
add some more libav api checks
m4: DRY up AX_CHECK_STATEMENT
require latest versions of autotools
configure.ac: add maintainer mode
fix AC_INIT call