Initial implementation of manual highlighting (#1087)
Initial implementation of manual highlighting (#1087)

* Initial implementation of manual highlighting

Borrow the `manual` property of whatever already existing Prism instance
there is.

* Simplify setting of `Prism.manual`

Cleans up the implementation w/ less code.

mAAdhaTTah/prism,MakeNowJust/prism,PrismJS/prism,byverdu/prism,byverdu/prism,byverdu/prism,MakeNowJust/prism,CupOfTea696/prism,mAAdhaTTah/prism,byverdu/prism,PrismJS/prism,mAAdhaTTah/prism,PrismJS/prism,mAAdhaTTah/prism,CupOfTea696/prism,CupOfTea696/prism,CupOfTea696/prism,CupOfTea696/prism,MakeNowJust/prism,MakeNowJust/prism,mAAdhaTTah/prism,byverdu/prism,PrismJS/prism,PrismJS/prism,MakeNowJust/prism