Add `loglogistic`, `logitexp`, `log1mlogistic` and `logit1mexp` #350

Job	Run time
Documentation	1m 2s
Julia 1.0 - ubuntu-latest - x64 - pull_request	4m 48s
Julia 1 - ubuntu-latest - x64 - pull_request	3m 53s
Julia nightly - ubuntu-latest - x64 - pull_request	4m 36s
	14m 19s

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