Add history::RecordManager class

This class will manage the records for the input power
history that has to be maintained on D-Bus.  This includes
the average power and maximum power over 30 second intervals.

The actual power values come from the power supply, and the
PowerSupply class will pass that data to this class every time
it is read, which is faster than the data actually changes since
it only changes every 30s.  This class will only save new data
when it has changed.

If there is new data available, this class will let the caller
know that it should then ask for the D-Bus property values for
the maximum and average power values, which are each arrays with
entries made up of timestamps along with the values.

This commit just includes some base functionality.  The rest will
come in future commits.

Change-Id: I1e521ba2ff7f733376b769ffa0d7053a0231d732
Signed-off-by: Matt Spinler <spinler@us.ibm.com>
diff --git a/power-supply/Makefile.am b/power-supply/Makefile.am
index 01f8b5e..862db7c 100644
--- a/power-supply/Makefile.am
+++ b/power-supply/Makefile.am
@@ -7,7 +7,8 @@
 witherspoon_psu_monitor_SOURCES = \
 	main.cpp \
 	argument.cpp \
-	power_supply.cpp
+	power_supply.cpp \
+	record_manager.cpp
 
 witherspoon_psu_monitor_CXXFLAGS = \
 	$(SDBUSPLUS_CFLAGS) \