Support setting target directory in `hugo gen man`
Support setting target directory in `hugo gen man`

Fixes #1627

Zenithar/hugo,fhergomez/hugo,fedelibre/hugo,kujohn/hugo,digitalcraftsman/hugo,mitchchn/hugo,bogem/hugo,anthonyfok/hugo,tubo028/hugo,tubo028/hugo,gohugoio/hugo,MarkDBlackwell/hugo,tatsushid/hugo,ifraixedes/hugo,fhergomez/hugo,sprig/hugo,fedelibre/hugo,ffrizzo/hugo,vbatoufflet/hugo,tischda/hugo,mitchchn/hugo,MarkDBlackwell/hugo,derekperkins/hugo,ryanclarke/hugo,sprig/hugo,jygastaud/hugo,mdhender/hugo,Zenithar/hugo,digitalcraftsman/hugo,anthonyfok/hugo,kujohn/hugo,soundrussian/hugo,ryanclarke/hugo,ifraixedes/hugo,abourget/hugo,gohugoio/hugo,coderzh/hugo,fedelibre/hugo,fedelibre/hugo,bramp/hugo,coderzh/hugo,melo/hugo,anthonyfok/hugo,jygastaud/hugo,tischda/hugo,melo/hugo,vbatoufflet/hugo,bogem/hugo,mayah/hugo,bramp/hugo,tatsushid/hugo,mayah/hugo,mdhender/hugo,mdhender/hugo,gohugoio/hugo,derekperkins/hugo,soundrussian/hugo,halostatue/hugo,abourget/hugo,halostatue/hugo,ffrizzo/hugo,mdhender/hugo