message: Add text super/sub script snippets, and fix underline & fontsize description
diff: | Prefix | Command |
  | ---------- | ------------------------------------------------------------------------------------------- |
  -| `fontsize` | `${1|\Huge,\huge,\LARGE,\Large,\large,\normalsize,\small,\footnotesize,\scriptsize,\tiny|}` |
  +| `fontsize` | Opens font size select |
  | `FNO` | `\textnormal{${1}}` |
  | `FRM` | `\textrm{${1}}` |
  | `FEM` | `\emph{${1}}` |
  | `FIT` | `\textit{${1}}` |
  | `FSL` | `\textsl{${1}}` |
  | `FSC` | `\textsc{${1}}` |
  -| `FUL` | `\upperline{${1}}` |
  +| `FUL` | `\underline{${1}}` |
  | `FUC` | `\uppercase{${1}}` |
  | `FLC` | `\lowercase{${1}}` |
  | `FBF` | `\textbf{${1}}` |
  -
  +| `FSS` | `\textsuperscript{${1}}` |
  +| `FBS` | `\textsubscript{${1}}` |
  ## Mathematical font commands
  