Bitbucket Markdown does not conform to the current CommonMark spec, per docs

The BB markdown syntax guide (https://confluence.atlassian.com/bitbucketserver/markdown-syntax-guide-776639995.html) does not conform to the cited CommonMark specs with regard to nested lists. CommonMark allows for only 2 spaces for sub lists, however Bitbucket requires 4 spaces. This creates significant output formatting issues when bringing in documents from other sources (most of which only use 2 spaces for sub lists).

Some examples of significant organizations that follow the two-space rule:

• Stack overflow
• GitHub
• CommonMark

Please fix the requirement and add Bitbucket to the list.

* item 1
* item 2
  * sub-item 1
  * sub-item 2
* item 3

should properly render a nested list under item 2