Add benchmarks

Author: blegat

test/perf/nl_alias_cache.jl

@@ -0,0 +1,18 @@
+Part of the problem is this horrific block:
+```
+@expression(household, betaks[r=R,s=S],
+    kd0[r,s]/sum(kd0[rr,ss] for rr∈R,ss∈S)
+)
+
+@expressions(household, begin
+    PI_KS, sum(betaks[r,s]*RK[r,s]^(1+etaK) for r∈R,s∈S)^(1/(1+etaK))
+    O_KS_RK[r=R,s=S], kd0[r,s]*(RK[r,s]/PI_KS)^etaK
+    I_RKS_KS, sum(kd0[r,s] for r∈R,s∈S)
+end)
+
+@constraint(household, prf_KS,
+    RKS*I_RKS_KS - sum(RK[r,s]*O_KS_RK[r,s] for r∈R,s∈S) ⟂ KS
+)
+```
+
+`|R|` is 51 and `|S|` is 71. So `PI_KS` contains $O(|R| \times |S|)$ terms. This appears in the denominator of `O_KS_RK`, and `O_KS_RK` appears `prf_KS` $O(|R| \times |S|)$ times. So the function has $O(|R|^2 \times |S|^2) = 13,111,641$ terms. Ouch.