This changes the design of the manifest.json file to have a separate
"folders" map for mapping hashed directories. This allows, for example,
to add files in a folder like `http_localhost_8000/#testing_5de71/` and
have them be resolved automatically as long as their remaining
components are identity-mappable to the file system (not hashed). It
also saves space in the manifest.json file by only including the hashed
directory instead of each descendant file.
```
// manifest.json
{
"folders": {
"https://localhost/NOT_MAPPABLE/": "localhost/#not_mappable_5cefgh"
},
"modules": {
"https://localhost/folder/file": {
"headers": {
"content-type": "application/javascript"
}
},
}
}
// folder structure
localhost
- folder
- #file_2defn (note: I've made up the hashes in these examples)
- #not_mappable_5cefgh
- mod.ts
- etc.ts
- more_files.ts
```
