Updated change_log for 2.6.2.
Updated change_log for 2.6.2.

cyisfor/Python-Markdown,cyisfor/Python-Markdown,gogobook/Python-Markdown,evertqin/Python-Markdown,me-and/Python-Markdown,me-and/Python-Markdown,evertqin/Python-Markdown,fernandezcuesta/Python-Markdown,gogobook/Python-Markdown,joachimneu/Python-Markdown,joachimneu/Python-Markdown,evertqin/Python-Markdown,waylan/Python-Markdown,gogobook/Python-Markdown,fernandezcuesta/Python-Markdown,cyisfor/Python-Markdown,waylan/Python-Markdown,fernandezcuesta/Python-Markdown,me-and/Python-Markdown,joachimneu/Python-Markdown