fix(r): credit kingchenc as R package author/maintainer (#332)

Every other binding (Python, Node, Rust core) credits kingchenc; the R
DESCRIPTION was an outlier with "Wickra contributors" as the sole
aut/cre, introduced when the binding was added (#230). Use kingchenc to
match, regenerate the package .Rd, and align the LICENSE copyright holder
with the root LICENSE-MIT ("kingchenc and the Wickra contributors").

bindings/r/man/wickra-package.Rd

@@ -24,11 +24,11 @@ Useful links:
 
 }
 \author{
-\strong{Maintainer}: Wickra contributors \email{support@wickra.org}
+\strong{Maintainer}: kingchenc \email{support@wickra.org}
 
 Authors:
 \itemize{
-  \item Wickra contributors \email{support@wickra.org}
+  \item kingchenc \email{support@wickra.org}
 }
 
 }