C++0x compatible exception semantics: remove throw()

Fixes #91.

Fix some warnings in the tests in Visual Studio

Added interpolation to WASAPI's sample rate converter

Pulseaudio backend also needs pthreads

Fix handling of CXXFLAGS in configure.ac.

CXXFLAGS should be set before AC_PROG_CXX.  This patch uses a syntax
allowing it to be overridden during "env CXXFLAGS=... ./configure",
"./configure CXXFLAGS=..." or during "make CXXFLAGS=..."

Keeps previous behaviour of -O3 for normal builds, -g -O0 for debug
builds, and keeps the define __RTAUDIO_DEBUG__, however this is done
using AC_DEFINE.

Port the build system to automake

Revert "duplex test: 64 bit compatibility"

Fix version and add version check

This reverts commit f639653f5e.

This change breaks the build with g++ 5.2.1 (Ubuntu 15.10).