Rename Screenshotter -> screenshotter (#1573)

Fix #1570

dockers/screenshotter/README.md

@@ -0,0 +1,75 @@
+# How to generate screenshotter images
+
+## Automatic generation of screenshots
+
+Now you too can generate screenshots from your own computer, and (hopefully)
+have them look mostly the same as the current ones! Make sure you have docker
+installed and running.
+If all you want is (re)create
+all the snapshots for all the browsers, then you can do so by:
+
+    yarn test:screenshots:update
+
+It will fetch all required selenium docker images, and use them to
+take screenshots.
+
+## Manual generation
+
+If you are creating screenshots on a regular basis, you can keep the
+docker containers with the selenium setups running.  Essentially you
+are encouraged to reproduce the steps from `screenshotter.sh`
+manually.  Example run for Firefox:
+
+    container=$(docker run -d -P selenium/standalone-firefox:2.46.0)
+    node dockers/screenshotter/screenshotter.js -b firefox -c ${container}
+    # possibly repeat the above command as often as you need, then eventually
+    docker stop ${container}
+    docker rm ${container}
+
+For Chrome, simply replace both occurrences of `firefox` with `chrome`.
+
+## Use without docker
+
+It is possible to run `screenshotter.js` without the use of Docker:
+
+    yarn add selenium-webdriver
+    node dockers/screenshotter/screenshotter.js
+
+This will generate screenshots using the Firefox installed on your system.
+Browsers other than Firefox can be targeted using the `--browser` option.
+For a complete list of options pass `--help` as an argument to
+`screenshotter.js`.  Using these it should be possible to have the script
+connect to almost any Selenium web driver you might have access to.
+
+Note that screenshots taken without Docker are very likely to disagree
+from the ones stored in the repository, due to different versions of
+various software components being used.  The screenshots taken in this
+fashion are well suited for visual inspection, but for exact binary
+comparisons it would be neccessary to carefully set up the environment
+to match the one used by the Docker approach.
+
+Screenshots can also be verified and generated by opening a pull request.
+Diffs and generated screenshots are available at the `Artifacts` section
+of CircleCI builds.
+
+## Choosing the list of test cases
+
+Both `screenshotter.js` and `screenshotter.sh` will accept
+an `--include` option (short `-i`) which can be used to specify
+a list of test cases to be processed, as a comma separated list.
+Conversely, the `--exclude` option (short `-x`) can be used
+to specify a list of cases which are not being processed.
+
+Examples:
+
+    node dockers/screenshotter/screenshotter.js -i Sqrt,SqrtRoot
+    dockers/screenshotter/screenshotter.sh --exclude=GreekLetters
+
+# How to run screenshotter tests
+
+You can verify screenshots by running:
+
+    yarn test:screenshots
+
+or passing `--verify` option to `screenshotter.js` or `screenshotter.sh`.
+See above for more details.