Remove compression & switch to imagick 7

Will chain with `compresspng` in lua, easier to set optimization
settings in tup config

README.md

@@ -7,7 +7,7 @@
 This project depends on
 
 - [tup](http://gittup.org/tup/)
-- [GraphicsMagick](http://www.graphicsmagick.org/)
+- [ImageMagick](http://www.imagemagick.org/)
 - [AdvPng](http://www.advancemame.it/doc-advpng.html)
 - [pnpm](https://pnpm.js.org)
 - [node.js](https://nodejs.org)
@@ -21,17 +21,19 @@ Windows binaries of these dependencies can be found on the download pages of the
 _**TODO:** include installation instructions for `tup` given the Ubuntu PPA is defunct_
 
 ```
-$ sudo apt install nodejs graphicsmagick advancecomp
+$ sudo apt install nodejs imagemagick advancecomp
 $ sudo npm install -g pnpm
 ```
 
+You may have to build imagemagick from source to get version 7.
+
 ### macOS
 
 Using [`brew`](https://brew.sh/) on  a macOS:
 
 ```
 $ brew cask install osxfuse
-$ brew install tup graphicsmagick advancecomp
+$ brew install tup imagemagick advancecomp
 ```
 
 ## Building

tools/fbsprite.sh

@@ -2,7 +2,4 @@
 
 # Smogdex Facebook social images
 
-set -e
-
-gm convert $1'[0]' -trim -resize 150x150 -background white -gravity center -extent 198x198 -bordercolor black -border 1 $2
-advpng -q -z $2
+convert $1'[0]' -trim -resize 150x150 -background white -gravity center -extent 198x198 -bordercolor black -border 1 $2

tools/padsprite.sh

@@ -2,7 +2,4 @@
 
 # input output w h
 
-set -e
-
-gm convert $1'[0]' -background transparent -gravity center -extent $3x$4 $2
-advpng -q -z $2
+convert $1'[0]' -background transparent -gravity center -extent $3x$4 $2

tools/twittersprite.sh

@@ -2,7 +2,4 @@
 
 # Smogdex Twitter social images
 
-set -e
-
-gm convert $1'[0]' -trim -resize 115x115 -background white -gravity center -extent 120x120 $2
-advpng -q -z $2
+convert $1'[0]' -trim -resize 115x115 -background white -gravity center -extent 120x120 $2