Thanks github user @bontric, closes #113.

Warnings/errors "unused function" are from the unicode conversion
functions on Windows, and "unused but set variable" is from ASIO
source code; we disable these warnings on Windows builds.

Revert "fix" for Issue #69

it's only cruft

afaict, the current code wouldn't work at all (defining an unused 'objects'
Makefile-variable).

consistent ordering of AC_MSG, additional library checks and var-setting.
also, use "=" rather than "=" when testing for equality

CPPFLAGS are needed to compile rtaudio.
these are not the same flags as needed for compiling an application using rtaudio.
sometimes this is even harmful.

Closes: https://github.com/thestk/rtaudio/issues/103

Signed-off-by: IOhannes m zmölnig <zmoelnig@umlautQ.umlaeute.mur.at>

Similar to edb4ec67.  The reason is because std::roundf causes errors
in some compilers even with cmath, yet roundf by itself should exist
in math.h.  TODO: Switch to std::round when moving to C++11.

Fixes #100.

add rtaudio c api wrappers