fix list rendering issue with strikethrough text

first 2.0 implementation - at least no error

theleague/commonmark 2.0.x compatibility matching

fix multiline indented code block rendering issue

fix escaping issue on indented code block

fix hr rendering error after list (#16)

fix escape option in inline / block code

Fix default code block process issue

add table syntax

add footnote support

support h6~ problem (treat all as h6)

fix default tag option

fix namespace & heading number

fix typo

revise descriptions

first working version