Add style to capitalize/lowercase text

[shitchell]

It would be awesome to be able to apply text transformations that manipulate capitalization, e.g.:

"heading": {
  "bold": true
},
"h1": {
  "upper": true,
},
"h3": {
  "lower": true
}

converts:

# This is a header
### This is a subheader

into:

THIS IS A HEADER

this is a subheader