add bitbucket server mode

[dstandish]

with bitbucket server, you have to add anchor tags e.g. <a name='this-heading'></a> for # This heading

[zhongxiao37]

I made a change in zhongxiao37@6d94c0d and it worked in my local.

[Greg7000]

To work on bitbucket server, TOC must generate anchors for each title. I can't have working links in bitbucket server.

See yzhang-gh/vscode-markdown#703 for more info on this.