What boards have integrated USB charging? I've been building wearables, using the adafruit trinket, which I love, its small size is easy to tuck away. But I hate having to unplug the battery to charge it every time. I wired in a SPDT switch, and a small USB charger, but it's kind of a cockamamie solution. 

I've seen some devices with a battery adapter, and integrated USB charging, 
but they are larger, and harder to tuck away.  

I don't need more than 4 IO ports, I'm just looking for a tiny microcontroller platform with integrated USB charging. I just saw the mkr1000 today, which looks decent, but is still larger than I would like. If you know of a product that meets this description, please let me know.
The Feather mainboards are fairly small and have integrated LiPo/Li-ion charging. They're not as small at the Trinket but if you don't need the space on the proto boards then you can examine the design files to see what can be cut away.