The way our markdown raw_html hoisting worked, we only
supported one level of hoisting the HTML content. However
when nesting [chat] transcript BBCode we need to allow
for multiple levels of it. This commit changes opts.discourse.hoisted
to be more constant, and the GUID keys that have the hoisted
content are only deleted by unhoistForCooked rather than
the cook function itself, which prematurely deletes them
when they are needed further down the line.
