The official Gmail app for your iPhone or iPad accommodates new update in version 2.1

Henceforth the new update available since March 27, 2013 includes performance improvements and bug fixes. This also means that, you now swipe left or right to move between messages without returning to the inbox, selecting a message in the inbox now enables edit mode.  

In fact once in edit mode, tap on messages to select them and then choose to archive, delete, or more, from the new actions bar.