js: mark JS standard as warnings, add semistandard maker (#505)
js: mark JS standard as warnings, add semistandard maker (#505)

Based on discussion in https://github.com/neomake/neomake/pull/345.
Closes #345.
bonds/neomake,euclio/neomake,datanoise/neomake,neomake/neomake,nerdrew/neomake,euclio/neomake,codeinabox/neomake,bonds/neomake,neomake/neomake,nerdrew/neomake