add easier model loading code

Author: zuhengxu

example/SyntheticTargets.jl

@@ -0,0 +1,29 @@
+using Distributions, Random, LinearAlgebra
+using LogDensityProblems
+using IrrationalConstants
+using Plots
+
+
+include("targets/banana.jl")
+include("targets/cross.jl")
+include("targets/neal_funnel.jl")
+include("targets/warped_gaussian.jl")
+
+
+function load_model(name::String)
+    if name == "Banana"
+        return Banana(2, 1.0, 10.0)
+    elseif name == "Cross"
+        return Cross()
+    elseif name == "Funnel"
+        return Funnel(2)
+    elseif name == "WarpedGaussian"
+        return WarpedGauss()
+    else
+        error("Model not defined")
+    end
+end
+
+LogDensityProblems.dimension(dist::ContinuousDistribution) = length(dist)
+LogDensityProblems.logdensity(dist::ContinuousDistribution, x) = logpdf(dist, x)
+