Implements support for ECDSA keys. Fixes #2163.

Thanks to @pahrohfit and @Tomoyuki-GH for previous efforts to implement
suport for this.

Co-Authored-By: Robert Dailey <rob@wargam.es>
Co-Authored-By: Tomoyuki-GH <55397638+Tomoyuki-GH@users.noreply.github.com>

AUTHORS.md

@@ -154,6 +154,7 @@ Authors
 * [Luca Olivetti](https://github.com/olivluca)
 * [Luke Rogers](https://github.com/lukeroge)
 * [Maarten](https://github.com/mrtndwrd)
+* [Mads Jensen](https://github.com/atombrella)
 * [Maikel Martens](https://github.com/krukas)
 * [Malte Janduda](https://github.com/MalteJ)
 * [Mantas Mikulėnas](https://github.com/grawity)
@@ -213,6 +214,7 @@ Authors
 * [Richard Barnes](https://github.com/r-barnes)
 * [Richard Panek](https://github.com/kernelpanek)
 * [Robert Buchholz](https://github.com/rbu)
+* [Robert Dailey](https://github.com/pahrohfit)
 * [Robert Habermann](https://github.com/frennkie)
 * [Robert Xiao](https://github.com/nneonneo)
 * [Roland Shoemaker](https://github.com/rolandshoemaker)