message: Update README.md to add vi/emacs keybindings as a feature and fix a typo in example code
  * Updated README.md to include vi and emacs keybindings as completed
  features.
  * Fixed typo in 'Using Variables' example code.
diff: @@ -35,6 +35,7 @@ Ion is a shell for UNIX platforms, and is the default shell in Redox. It is stil
  - [x] Background Jobs
  - [x] Multiline Comments and Commands
  - [x] Tab Completion (Needs Improvements)
  +- [x] vi and emacs keybindings (`set -o (vi|emacs)`)
  ## Unimplemented Features
  @@ -76,8 +77,8 @@ They may also be optionally defined using a braced syntax, which is useful in th
  integrated alongside other characters that do not terminate the variable parsing.
  ```ion
  -let a = one
  -let b = two
  +let A = one
  +let B = two
  echo $A:$B
  echo ${A}s and ${B}s
  ```
  