update .gitignore to exclude exe files

.gitignore

@@ -21,3 +21,32 @@
 *.i*86
 *.x86_64
 *.hex
+
+# Example executables
+/dtls/client-dtls-nonblocking
+/dtls/client-dtls-resume
+/dtls/client-dtls
+/dtls/client-udp
+/dtls/server-dtls-nonblocking
+/dtls/server-dtls-threaded
+/dtls/server-dtls
+/dtls/server-udp
+
+/psk/client-psk-nonblocking
+/psk/client-psk-resume
+/psk/client-psk
+/psk/client-tcp
+/psk/server-psk-nonblocking
+/psk/server-psk-threaded
+/psk/server-psk
+/psk/server-tcp
+
+/tls/client-tls-nonblocking
+/tls/client-tls-resume
+/tls/client-tls
+/tls/client-tcp
+/tls/server-tls-nonblocking
+/tls/server-tls-threaded
+/tls/server-tls
+/tls/server-tcp
+