update RSS and add atom feed

Gemfile.lock

@@ -5,10 +5,11 @@ GEM
       public_suffix (>= 2.0.2, < 5.0)
     colorator (1.1.0)
     concurrent-ruby (1.1.7)
-    em-websocket (0.5.1)
+    em-websocket (0.5.2)
       eventmachine (>= 0.12.9)
       http_parser.rb (~> 0.6.0)
     eventmachine (1.2.7)
+    fastimage (2.2.0)
     ffi (1.13.1)
     forwardable-extended (2.6.0)
     http_parser.rb (0.6.0)
@@ -29,6 +30,9 @@ GEM
       rouge (~> 3.0)
       safe_yaml (~> 1.0)
       terminal-table (~> 1.8)
+    jekyll-image-size (1.2.1)
+      fastimage (>= 1.8)
+      jekyll (>= 3.7)
     jekyll-last-modified-at (1.1.0)
       jekyll (>= 3.7, < 5.0)
       posix-spawn (~> 0.3.9)
@@ -43,7 +47,7 @@ GEM
     kramdown-parser-gfm (1.1.0)
       kramdown (~> 2.0)
     liquid (4.0.3)
-    listen (3.2.1)
+    listen (3.3.1)
       rb-fsevent (~> 0.10, >= 0.10.3)
       rb-inotify (~> 0.9, >= 0.9.10)
     mercenary (0.4.0)
@@ -55,7 +59,7 @@ GEM
     rb-inotify (0.10.1)
       ffi (~> 1.0)
     rexml (3.2.4)
-    rouge (3.23.0)
+    rouge (3.25.0)
     safe_yaml (1.0.5)
     sassc (2.4.0)
       ffi (~> 1.9)
@@ -68,6 +72,7 @@ PLATFORMS
 
 DEPENDENCIES
   jekyll (= 4.1.1)
+  jekyll-image-size
   jekyll-last-modified-at (= 1.1.0)
   jekyll-sitemap (= 1.4.0)