Optimize markdown conversion
Optimize markdown conversion

Significantly reduces the memory usage of Markdown parser by
calling md.reset() in every iteration when using the same instance
of Markdown. This also provides huge speed boost when run
against database which has existing rows.

suutari-ai/shoop,shoopio/shoop,suutari-ai/shoop,suutari-ai/shoop,shoopio/shoop,shoopio/shoop