docs: add cid-base and missing ls options for mfs operations

Documents the new options added by ipfs/js-ipfs#1454 as well as the missing `long` option from `files.ls`

Author: achingbrain

SPEC/FILES.md

@@ -696,6 +696,7 @@ Where:
   - `hash` is a Boolean value to return only the hash  (default: false)
   - `size` is a Boolean value to return only the size  (default: false)
   - `withLocal` is a Boolean value to compute the amount of the dag that is local, and if possible the total size  (default: false)
+  - `cidBase` is which number base to use to format hashes - e.g. `base32`, `base64` etc (default: `base58btc`)
 - `callback` is an optional function with the signature `function (error, stats) {}`, where `error` may be an Error that occured if the operation was not successful and `stats` is an Object with the following keys:
 
 - `hash` is a string with the hash
@@ -970,11 +971,14 @@ ipfs.files.flush('/', (err) => {
 
 ##### `Go` **WIP**
 
-##### `JavaScript` - ipfs.files.ls([path], [callback])
+##### `JavaScript` - ipfs.files.ls([path], [options], [callback])
 
 Where:
 
 - `path` is an optional string to show listing for (default: `/`)
+- `options` is an optional Object that might contain the following keys:
+  - `long` is a Boolean value to decide whether or not to populate `type`, `size` and `hash` (default: false)
+  - `cidBase` is which number base to use to format hashes - e.g. `base32`, `base64` etc (default: `base58btc`)
 - `callback` is an optional function with the signature `function (error, files) {}`, where `error` may be an Error that occured if the operation was not successful and `files` is an array containing Objects that contain the following keys:
 
 - `name` which is the file's name