Markdown should not mangle explicit List Index

When writing out normal text that starts with a number and period, the markdown processing reindexes the number. This is unexpected as it is just normal text. I think reindexing should only happen if the first item starts with 1.

1. do this

2. do that

Currently, it will result in:

1. do this

1. do that

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mangle, trample, cc gitterHQ/marked#6

Created by: ai

I need it too. It is very useful, when you try explain benefits of your point.