Add `loglogistic`, `logitexp`, `log1mlogistic` and `logit1mexp` #351

Job	Run time
Documentation	1m 4s
Julia 1.0 - ubuntu-latest - x64 - pull_request	3m 36s
Julia 1 - ubuntu-latest - x64 - pull_request	2m 30s
Julia nightly - ubuntu-latest - x64 - pull_request	3m 7s
	10m 17s

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