Replace GraphicsMagick with sharp

That was easier than I expected.

Closes #18.

src/site/api/proxy.js

@@ -1,7 +1,7 @@
 const constants = require("../../lib/constants")
 const {request} = require("../../lib/utils/request")
 const {proxy} = require("pinski/plugins")
-const gm = require("gm")
+const sharp = require("sharp")
 
 module.exports = [
 	{route: "/imageproxy", methods: ["GET"], code: async (input) => {
@@ -23,36 +23,24 @@ module.exports = [
 		const width = +params.get("width")
 		if (typeof width === "number" && !isNaN(width) && width > 0) {
 			/*
-				This uses graphicsmagick to force crop the image to a square.
-				Some thumbnails aren't square and will be stretched on the page without this.
+				This uses sharp to force crop the image to a square.
+				"entropy" seems to currently work better than "attention" on the thumbnail of this shortcode: B55yH20gSl0
+				Some thumbnails aren't square and would otherwise be stretched on the page without this.
 				If I cropped the images client side, it would have to be done with CSS background-image, which means no <img srcset>.
 			*/
 			return request(url).then(res => {
-				const image = gm(res.body).gravity("Center").crop(width, width, 0, 0).repage("+")
+				const converter = sharp().resize(width, width, {position: "entropy"})
 				return {
 					statusCode: 200,
 					contentType: "image/jpeg",
 					headers: {
 						"Cache-Control": constants.caching.image_cache_control
 					},
-					stream: image.stream("jpg")
+					stream: res.body.pipe(converter)
 				}
-				/*
-					Alternative buffer-based method for sending file:
-
-					return new Promise(resolve => {
-						image.toBuffer((err, buffer) => {
-							if (err) console.error(err)
-							resolve({
-								statusCode: 200,
-								contentType: "image/jpeg",
-								content: buffer
-							})
-						})
-					})
-				*/
 			})
 		} else {
+			// No specific size was requested, so just stream proxy the file directly.
 			return proxy(url, {
 				"Cache-Control": constants.caching.image_cache_control
 			})