Add generic signal handling API to work with boost::asio

This allows providers or the main application to handle POSIX signals
using a callback chain. Each handler can return continueExecution or
breakExecution to stop the signal handling chain or allow it to
continue. Each handler is registered with a priority and upon reciept of
a signal, each handler is executed in priority order until the end of
the list is reached or one returns with breakExecution.

Change-Id: Idd83625eb1a2d3bdafc92bdd839e0d6386177ff2
Signed-off-by: Vernon Mauery <vernon.mauery@linux.intel.com>
diff --git a/libipmid/Makefile.am b/libipmid/Makefile.am
index ac35bbf..e4899e1 100644
--- a/libipmid/Makefile.am
+++ b/libipmid/Makefile.am
@@ -13,6 +13,7 @@
 lib_LTLIBRARIES = libipmid.la
 libipmid_la_SOURCES = \
 	sdbus-asio.cpp \
+	signals.cpp \
 	systemintf-sdbus.cpp
 libipmid_la_LDFLAGS = \
 	$(SYSTEMD_LIBS) \