The Redstone Update was announced at the Future Updates with the Minecraft PC Team and The Future of Mod API talks at MINECON 2012.[1]
Development began shortly after 1.4.6 was released. Sixteen development snapshots were released, from 13w01a to 13w10b, with a few snapshots being quickly re-released straight after to fix bugs without changing the client version number. During the development period, 1.4.7 was released. Nearer the end of the snapshot cycle for the 1.5 update, Mojang focused primarily on fixing bugs, rather than adding new features.
Mojang originally planned to release a pre-release version of The Redstone Update on February 28, 2013, and the official update in the first week of March.[2] However, the pre-release was delayed as Mojang was trying to fix more bugs before a stable release,[3][4] and was subsequently released on March 7.
1.5.1 gave the players the ability to combine enchanted books to get a higher enchantment level, and allowed hoppers to take empty buckets out of furnace fuel slots and fixed performance issues.
1.5.2 fixed bugs, crashes and additional performance issues.