Various fixes for source-position information#210

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QuietMisdreavus wants to merge 3 commits intogithub:masterfrom

QuietMisdreavus:sourcepos-fixes

Commits on Jan 27, 2021

apply block offsets for autolink source position info
QuietMisdreavus
committed
don't let blocks get end lines before their start lines
QuietMisdreavus
committed
properly set image/link sourcepos when spanning multiple lines
QuietMisdreavus
committed