Update docs for new async pouch creation

docs/api.md

@@ -43,17 +43,14 @@ Retrieves all databases from PouchDB.
 
 ## Create a database
 
-    Pouch('dbname', [options], [callback])
-    Pouch('http://localhost:5984/dbname', [options], [callback])
+    var pouchdb = Pouch('dbname', [options])
+    var pouchdb = Pouch('http://localhost:5984/dbname', [options])
 
 This method gets an existing database if one exists or creates a new one if one does not exist. You may also explicitly specify which backend you want to use for local database (e.g. `idb://dbname` or `leveldb://dbname`) but usually it is convenient to let PouchDB choose the best backend by itself.
 
-    var pouchdb;
-    Pouch('test', function(err, db) {
-      pouchdb = db;
-      // Use pouchdb to call further functions
-      pouchdb.post(....
-    })
+    var pouchdb = Pouch('test');
+
+    pouchdb.post(...;
 
 ## Delete a database
 
@@ -243,7 +240,7 @@ Fetch multiple documents, deleted document are only included if `options.keys` i
 * `options.keys`: array of keys you want to get
     - neither `startkey` nor `endkey` can be specified with this option
     - the rows are returned in the same order as the supplied "keys" array
-    - the row for a deleted document will have the revision ID of the deletion, and an extra key "deleted":true in the "value" property 
+    - the row for a deleted document will have the revision ID of the deletion, and an extra key "deleted":true in the "value" property
     - the row for a nonexistent document will just contain an "error" property with the value "not_found"
 * `options.attachments`: Include attachment data
 
@@ -415,7 +412,7 @@ If `options.continuous` is set it returns object with one method `cancel` which
 * `options.since`: Start the results from the change immediately after the given sequence number
 * `options.complete`: Function called when all changes have been processed
 * `options.continuous`: Use _longpoll_ feed
-* `options.onChange`: Function called on each change after deduplication (only sends the most recent for each document), not called as a callback but called as onChange(change). Use with `continuous` flag. If you want to 
+* `options.onChange`: Function called on each change after deduplication (only sends the most recent for each document), not called as a callback but called as onChange(change). Use with `continuous` flag. If you want to
 
 <span></span>
 
@@ -506,7 +503,7 @@ Replicate one database to another.
 
     db.revsDiff(diff, [callback])
 
-Given a set of document/revision IDs, returns the subset of those that do not correspond 
+Given a set of document/revision IDs, returns the subset of those that do not correspond
 to revisions stored in the database. Primarily used in replication.
 
     db.revsDiff({