add swift and crystal to implementations (#36)

Author: danini-the-panini

src/_includes/partials/implementations.md

@@ -19,6 +19,8 @@
 * Nim: [kdl-nim](https://github.com/Patitotective/kdl-nim)
 * Common Lisp: [kdlcl](https://github.com/chee/kdlcl)
 * Go: [gokdl](https://github.com/lunjon/gokdl), [kdl-go](https://github.com/sblinch/kdl-go)
+* Swift: [kdl-swift](https://github.com/danini-the-panini/kdl-swift)
+* Crystal: [kdl-cr](https://github.com/danini-the-panini/kdl-cr)
 
 ## Editor Support