THANKS: added contributors from 7.21.3

docs/THANKS

@@ -30,6 +30,7 @@ Alexey Borzov
 Alexey Pesternikov
 Alexey Simak
 Alexis Carvalho
+Alfred Gebert
 Allen Pulsifer
 Amol Pattekar
 Anatoli Tubman
@@ -199,6 +200,7 @@ Dimitris Sarris
 Dinar
 Dirk Eddelbuettel
 Dirk Manske
+Dmitri Shubin
 Dmitriy Sergeyev
 Dmitry Bartsevich
 Dmitry Kurochkin
@@ -307,10 +309,12 @@ Hardeep Singh
 Harshal Pradhan
 Hauke Duden
 Heikki Korpela
+Heinrich Ko
 Hendrik Visage
 Henrik Storner
 Hidemoto Nakada
 Hoi-Ho Chan
+Hongli Lai
 Howard Chu
 Hzhijun
 Ian Ford
@@ -522,6 +526,7 @@ Matt Witherspoon
 Matt Wixson
 Matthew Blain
 Matthew Clarke
+Matthias Bolte
 Maurice Barnum
 Mauro Iorio
 Max Katsev
@@ -695,6 +700,7 @@ Rosimildo da Silva
 Roy Shan
 Rune Kleveland
 Ruslan Gazizov
+Rutger Hofman
 Ryan Chan
 Ryan Nelson
 S. Moonesamy
@@ -735,6 +741,7 @@ Stan van de Burgt
 Stefan Esser
 Stefan Krause
 Stefan Teleman
+Stefan Tomanek
 Stefan Ulrich
 Stephan Bergmann
 Stephen Collyer