Changed type info to be retrieved from name tag instead of struct tag

Originally, I had type info encoded in the struct tag. This initially
made sense because the type info only directly impacts the struct tag.
However this was a case of focusing too much on the details instead of
the bigger picture.

A more file operations need to figure out the type of a file, but it's
only actually a small number of file operations that need to interact
with the file's structure. For the common case, providing the type of
the file early shortens operations by a full tag access.

Additionally, but storing the type in the file name tag, this opens up
the struct tag to use those bits for storing more struct descriptions.