Description of importing the codemirror library into Moodle.

NOTE: To make it more readable, in this explanation [LIBRARYPATH] means:
    [PATH TO YOUR MOODLE]/lib/editor/atto/plugins/html/yui/src/codemirror

1 Download the latest codemirror code somewhere (example /tmp/cm) using:

mkdir -p codemirror/node_modules
npm install --prefix codemirror codemirror@5 --save-dev

Note down the version number displayed by the command, to update thirdpartylibs.xml accordingly.

2 Then copy the following files to your local Moodle directory:

[CODEMIRRORPATH] = codemirror/node_modules

cp [CODEMIRRORPATH]/codemirror/lib/codemirror.js [LIBRARYPATH]/js
cp [CODEMIRRORPATH]/codemirror/mode/css/css.js [LIBRARYPATH]/js
cp [CODEMIRRORPATH]/codemirror/mode/htmlmixed/htmlmixed.js [LIBRARYPATH]/js
cp [CODEMIRRORPATH]/codemirror/mode/javascript/javascript.js [LIBRARYPATH]/js
cp [CODEMIRRORPATH]/codemirror/mode/xml/xml.js [LIBRARYPATH]/js

3 Rebuild the module by:
    cd [PATH TO YOUR MOODLE]/lib/editor/atto/plugins/html/yui/src/
    grunt shifter

4 Update the version number in (using the version noted down in #1):
    [PATH TO YOUR MOODLE]/lib/editor/atto/plugins/html/thirdpartylibs.xml