added NaN test for asin
added NaN test to agrad/fwd/asin
updated NaN test for agrad/rev/asin
switched to no namespace version of asin
updated bound tests for asin
added NaN and derivative doc for asin in manual
updated fwd/matrix tests
Merge branch 'develop' into feature/test-nan-asin

Conflicts:
	src/docs/stan-reference/appendices.tex
Merge branch 'develop' into feature/test-nan-asin

Conflicts:
	doc/stan-reference-2.4.0.pdf
	src/docs/stan-reference/appendices.tex
Merge pull request #949 from stan-dev/feature/test-nan-asin

Feature/test nan asin