e523f99fb9
This modifies the command-line usage of rustdoc to intake its own JSON output as well as a rust source file. This also alters the command line from `rustdoc input file` to `rustdoc file` with the input/output formats specified as -r and -w, respectively. When using a JSON input, no passes or plugins are re-run over the json, instead the output is generated directly from the JSON that was provided. Passes and plugins are still run on rust source input, however.