Add `loglogistic`, `logitexp`, `log1mlogistic` and `logit1mexp` #337

Job	Run time
Documentation	1m 0s
Julia 1.0 - ubuntu-latest - x64 - pull_request	4m 42s
Julia 1 - ubuntu-latest - x64 - pull_request	3m 46s
Julia nightly - ubuntu-latest - x64 - pull_request	4m 33s
	14m 1s

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