NB: Extension is still under development
This changes the behaviour of the enter key in whatsapp web.
To install the extension off-store, download the latest release as a zip file from the Releases page, or better, just clone the source code to a directory and add it to Chrome using the 'Load unpacked extension' option when developer mode is turned on.
This is more experimental and has been tested on Chrome only.
No data is ever transmitted to anywhere.