Improve replication functions

[wleoncio]

• Fix pseudo-strata for odd-numbered PSUs
• Cap number of replications at 80
• Allow customization of # of reps on BRR
• Loop pseudo-strata if reps < PSUs on BRR
• Sort schools by size before pairing them into pseudo-strata (BRR)
• Add Jackknife 2 (Jackknife with pseudo-strata and 2/0 weights)