Support folders for serving content

[bgrainger]

I'm trying to use XmlDocMarkdown with a Hugo site (defined here: https://github.com/mysql-net/MySqlConnector/tree/master/docs)

So far, I've gotten the best results with this command line:

xmldocmd --front-matter .\docs\front-matter.yml --clean --namespace-pages --permalink pretty .\src\MySqlConnector\bin\Release\netcoreapp3.0\MySqlConnector.dll docs\content\api\MySqlConnector\

However, the links in the generated files aren't correct, as they assume that the page will be served from /api/MySqlConnector/MySqlConnectorAssembly.html instead of /api/MySqlConnector/MySqlConnectorAssembly/. Thus, a relative link goes to /api/MySqlConnector/MySqlConnectorAssembly/MySql.Data.MySqlClient/MySqlConnectionType (which 404s) when it should be /api/MySqlConnector/MySql.Data.MySqlClient/MySqlConnectionType/.

I've fixed the generated links in this commit, although I suspect there would be a more elegant way to do it: https://github.com/bgrainger/XmlDocMarkdown/commit/7e572ce18430d524b62a4f8259affdf20e33cbd8.

This may relate to https://github.com/ejball/XmlDocMarkdown/issues/77.