Use module name from @module tag

[MarkTiedemann]

Currently, deno doc --html requires the module name as an argument.

> deno doc --html mod.ts
error: the following required arguments were not provided:
  --name=<name>

I think the name could be optional if the module provides the name via JSDoc @module.

[crowlKats]

I dont think thats entirely a viable solution, however the underlying name is optional and as such we should make the name flag optional