Strikethrough text matching rule for quickmark.
const strikethrough = require('quickmark-rule-strikethrough');
strikethrough('~~i am no longer relevant~~');
// {
// original: '~~i am no longer relevant~~',
// parsed: 'i am no longer relevant'
// }
strikethrough('~~i am no longer relevant~~ but i still am');
// {
// original: '~~i am no longer relevant~~',
// parsed: 'i am no longer relevant'
// }
strikethrough('plain text');
// undefined