Build system improvements

Please pull my master branch to receive some improvements to the iniparser build system.  Currently, distributions must patch the Makefile or apply a command-line override to apply distribution-specific CFLAGS.  Some of the flags are worth keeping (-fPIC -Wall), so a command-line override is suboptimal.  This change picks up the user's $CFLAGS (if any) or uses -O2 (if no $CFLAGS is set), then appends the other iniparser options.  In most cases, this will remove the distribution's need to patch the Makefile.  A similar improvement is done for $LDFLAGS.  Commit #2 allows $CPPFLAGS to be included automatically, since the default definition of $COMPILE.c includes them.  Commit #3 is a linker command line cleanup.  Commit #4 makes it possible to switch between silent (default) and traditionally verbose builds without editing the Makefile.  Commit #5 makes it easier for C++ programs to link to libiniparser (but makes no attempt to build libiniparser as a C++ library).