2.0.0

• 6a02049 Change math to a function that returns an extension

   import {math, mathHtml} from 'micromark-extension-math'
  
   const output = micromark(fs.readFileSync('example.md'), {
  -  extensions: [math],
  +  extensions: [math()],
     htmlExtensions: [mathHtml()]
   })

• 522b6e1 Add singleDollarTextMath option