Implementation of Robust Adaptive Metropolis #307

Job	Run time
test (1.6, ubuntu-latest, x86)	2m 25s
test (1.6, ubuntu-latest, x64)	2m 1s
test (1.6, macOS-latest, x64)	2m 57s
test (1.6, windows-latest, x86)	14m 37s
test (1.6, windows-latest, x64)	10m 4s
test (1, ubuntu-latest, x86)	3m 7s
test (1, ubuntu-latest, x64)	2m 22s
test (1, macOS-latest, x64)	4m 47s
test (1, windows-latest, x86)	4m 26s
test (1, windows-latest, x64)	3m 32s
test (nightly, ubuntu-latest, x86)	3m 21s
test (nightly, ubuntu-latest, x64)	2m 39s
test (nightly, macOS-latest, x64)	4m 55s
test (nightly, windows-latest, x86)	4m 30s
test (nightly, windows-latest, x64)	3m 35s
	1h 9m 18s

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