Document fast powers in IA

[mforets]

Using the nonrecursive_powers branch from IntervalArithmetic gives a nice speedup; we should document it (if possible make it our default choice, see JuliaIntervals/IntervalArithmetic.jl#355).

cc: @dpsanders

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Examples:

1) Lotka-Volterra with tangential crossing (showing only the computation of the first flowpipe):

# using IntervalArithmetic#master
   2.117550 seconds (11.04 M allocations: 628.267 MiB, 5.26% gc time) 

# using IntervalArithmetic#nonrecursive_powers
  1.102706 seconds (8.08 M allocations: 494.141 MiB, 9.57% gc time) 

2) Production-Destruction with uncertain IC

using IntervalArithmetic#master

@time sol1 = solve(prob, tspan=(0.0, 100.0), alg=TMJets(orderT=7, orderQ=1, abs_tol=1e-12));
  3.883992 seconds (47.52 M allocations: 2.808 GiB, 19.66% gc time)

tspan(X) = [99.1936, 100]
X ⊆ positive_orthant = true
volume(H) = 4.363464432248047e-20
10 ∈ sum(B) = true
true

using IntervalArithmetic#nonrecursive_powers

# using IntervalArithmetic#nonrecursive_powers
  1.788210 seconds (38.75 M allocations: 2.435 GiB, 24.66% gc time)

tspan(X) = [99.2048, 100]
X ⊆ positive_orthant = true
volume(H) = 3.7004693455099e-20
10 ∈ sum(B) = true
true

I would have expected the opposite, but the volume is actually a bit smaller.

(*) In the "new" results (those with nonrecursive_powers branch) i also moved to TaylorModels#master, while i can't assure i was indeed running the latest version previously, or i was missing the optimization from this PR.

3) Production-Destruction with uncertain IC and uncertain parameters

using IntervalArithmetic#master

@time sol2 = solve(prob, tspan=(0.0, 100.0), alg=TMJets(orderT=7, orderQ=1, adaptive=true, abs_tol=1e-12));
  4.935956 seconds (85.01 M allocations: 5.131 GiB, 23.47% gc time)

tspan(X) = [99.5369, 100]
X ⊆ positive_orthant = true
volume(H) = 6.6200725506016844e-21
10 ∈ sum(B) = true
true

using IntervalArithmetic#nonrecursive_powers

# using IntervalArithmetic#nonrecursive_powers
  3.480925 seconds (76.07 M allocations: 4.832 GiB, 26.65% gc time)

tspan(X) = [99.9736, 100]
X ⊆ positive_orthant = true
volume(H) = 6.570202463333817e-21
10 ∈ sum(B) = true

4) Quadcopter (width 0.8)

# using IntervalArithmetic#master
 2.917486 seconds (41.88 M allocations: 2.539 GiB, 23.41% gc time)

# using IntervalArithmetic#nonrecursive_powers
  1.279259 seconds (29.45 M allocations: 2.044 GiB, 27.38% gc time)