Issue title: How to set tab width ?
 Issue body: monaco-editor npm version: 0.7.0
Browser: Chrome 54.0.2840.99 
OS: Windows 10


I want custom code tab width, use 2 spaces or 8 spaces.


 Comments: 
 Comment 0: Paging @alexandrudima.
 Comment 1: [`model.updateOptions({ tabSize: 8 })`](https://microsoft.github.io/monaco-editor/api/interfaces/monaco.editor.imodel.html#updateoptions). You can create a model yourself via [`monaco.editor.createModel(...)`](https://microsoft.github.io/monaco-editor/api/modules/monaco.editor.html#createmodel) or use the one created by the editor on your behalf [`editor.getModel()`](https://microsoft.github.io/monaco-editor/api/interfaces/monaco.editor.istandalonecodeeditor.html#getmodel)
 Comment 2: Thanks a lot!
 Comment 3: @alexandrudima Is your solution deprecated now? Because for me it works when I call `updateOptions` on the editor itself, not on the model.
 Comment 4: @chinchang seems that tabSize is a language consideration rather than the editor itself: 
https://microsoft.github.io/monaco-editor/api/interfaces/monaco.languages.formattingoptions.html
 Comment 5: @chinchang `tabSize` is a model property, so one must call `updateOptions` on the model instance in order to change `tabSize`.
{'source': 'GithubIssues', 'repo_name_with_owner': 'Microsoft/monaco-editor', 'issue_id': 190637666, 'repo_stars': 14765.0}