Support Atom editor setting conversion

[JoshuaKGoldberg]

🚀 Feature Request

#250 added an --editor feature to convert VS Code's TSLint extension settings to the VS Code ESLint equivalents. It'd be lovely to have a similar option for Atom: if a settings file for it exists, it should be converted.

Existing Behavior

tslint-to-eslint-config only looks for and supports the VS Code syntax for now.

Change Proposal

Whatever Atom uses (this?) should be supported as well. If either config file exists, its respective conversion should be attempted.

[JoshuaKGoldberg]

Taking a deeper look here, https://github.com/AtomLinter/linter-tslint supports three configuration options:

'linter-tslint':
  # Custom rules directory (absolute path)
  rulesDirectory: "/path/to/rules"
  # Try using the local tslint package (if exist)
  useLocalTslint: true
  # Enable semantic rules
  enableSemanticRules: true

The ESLint equivalent is https://github.com/AtomLinter/linter-eslint, which seems to have the following:

"linter-eslint":
    advanced:
      disableEslintIgnore: true
      disableFSCache: true
    autofix:
      fixOnSave: true
      ignoreFixableRulesWhileTyping: true
    global:
      useGlobalEslint: true
    lintHtmlFiles: true

So, I think the only option shared between them is useLocalTslint -> global.useGlobalEslint (as opposite values).