rtmidi can now easily be nested into another project

Makefile.am

@@ -1,3 +1,4 @@
-noinst_LIBRARIES = %D%/librtmidi.a
-librtmidi_a_SOURCES = %D%/RtMidi.cpp \
-                       %D%/RtMidi.h
+noinst_LIBRARIES += %D%/librtmidi.a
+%C%_librtmidi_a_SOURCES = \
+  %D%/RtMidi.cpp \
+  %D%/RtMidi.h

configure.ac

@@ -7,6 +7,7 @@ AM_INIT_AUTOMAKE([-Wall -Werror foreign subdir-objects])
 
 # Fill GXX with something before test.
 AC_SUBST( GXX, ["no"] )
+AC_SUBST(noinst_LIBRARIES)
 
 # Checks for programs.
 AC_PROG_CXX(g++ CC c++ cxx)