Pocket & StumbleUpon icons (#121)

* added pinboard

* fixed corner radius

* added pocket and stumbleupon

* fixed reference file extension

* removed width/height

* updated README

* shrink with svgo -p 1

* Update stumbleupon.svg

Add role.

* Update pocket.svg

Add role

* Update README.md

Updated sizes

images/svg/pocket.svg

@@ -0,0 +1,6 @@
+<svg xmlns="http://www.w3.org/2000/svg"
+aria-label="Pocket" role="img"
+viewBox="0 0 512 512"><rect
+width="512" height="512"
+rx="15%"
+fill="#e84352"/><path fill="#fff" d="M388.8 88.9H123.2A47.4 47.4 0 0 0 76 136.5v131.9c0 2.4.2 4.8.5 7.2a101.8 101.8 0 0 0-.5 10.6c0 75.6 80.6 137 180 137s180-61.4 180-137c0-3.6-.2-7.1-.5-10.6.3-2.4.5-4.8.5-7.2v-132A47.4 47.4 0 0 0 388.8 89zm-22.4 132.6l-93 93c-4.7 4.6-11 7-17.1 7a23.8 23.8 0 0 1-17.7-7l-93-93a24 24 0 0 1 33.8-33.8l76.6 76.5 76.6-76.5a24 24 0 0 1 33.8 33.8z"/></svg>

images/svg/stumbleupon.svg

@@ -0,0 +1,6 @@
+<svg xmlns="http://www.w3.org/2000/svg"
+aria-label="StumbleUpon" role="img"
+viewBox="0 0 512 512"><rect
+width="512" height="512"
+rx="15%"
+fill="#ea4b24"/><path fill="#fff" d="M362.2 397c-47.3 0-88.7-37.3-89-83.4v-59.2l29.4 22.6 33.5-24v61.6c0 10.9 14.7 20.6 26 20.6s21.9-9.7 21.9-20.6v-62.2h64v60.4a85 85 0 0 1-85.8 84.2zM256 173.8c-11.2 0-16.3 8.8-16.3 19.8V314c-.8 46.1-42.8 83-89.8 83A85 85 0 0 1 64 312.9v-59.6h63.3v59c0 10.8 11.5 19.8 22.7 19.8 11.3 0 25.2-9 25.2-19.9V190.3C176.7 145 210.7 109 257 109c46.6 0 77.5 36.3 79 81.7v26.8L306.7 236l-33.3-19.1v-23.3c0-11-6.2-19.8-17.4-19.8z"/></svg>