Started work towards the new Metric interface
Use SCons as the build tool instead of make
Merge branch 'master' into Metrics
New Metric interface that uses obs and forecasts only.

Metric only takes Obs and Forecast as input and produces a Score
	modified:   src/Metrics/*
	modified:   src/Score.*

Output class now stores and writes Score objects
	modified:   src/Outputs/Netcdf.cpp
	modified:   src/Outputs/Output.*

Removed MetricMae (use MetricNorm instead)
	modified:   namelists/default/schemes.nl
	deleted:    src/Metrics/Mae.cpp
	deleted:    src/Metrics/Mae.h

Created a MetricBasic class for simple fcst/obs metrics
	modified:   src/Metrics/Bias.*
	modified:   src/Metrics/Contingency.*
	modified:   src/Metrics/Forecast.*
	modified:   src/Metrics/Obs.*
	modified:   src/Metrics/Norm.*
	modified:   src/Metrics/Threshold.*

Created an object that contains det, ens, and dist entities for one point
	new file:   src/Forecast.cpp