added NaN test for inv_cloglog
added NaN test for inv_cloglog
added NaN and derivative doc for inv_cloglog to manual
Merge branch 'develop' into feature/test-nan-invcloglog
Merge branch 'develop' into feature/test-nan-invcloglog

Conflicts:
	src/docs/stan-reference/appendices.tex
Merge pull request #989 from stan-dev/feature/test-nan-invcloglog

Feature/test nan invcloglog