GitHub-like symbols panel

Looking at the Symbols panel on GitHub made me to want to implement (copy) my own.

Pet peeve

CodeMirror documentation is so scarce.

Issues

• Editor loads very slowly
• When definition or references are selected, selected line is not highlighted in the editor view
• Arrow functions are not collected in Symbols
  • Need to use ArrowFunctionExpression along with FunctionDeclaration inside traverse()
  • Need to access function name with path.container.id.name rather than path.node.id.name