Multiline authoring

[DunLug]

Hello,
I added an option to put authors of an IEEE paper on multiple lines, when there is too many authors.
The authors definition is in the yaml section of Index.Rmd this way:

- affiliation:
  - author_multiline:
    - line:
      - name: Author 1
      - name: Author 2
    - line:
      - name: Author 3
      - name: Author 4

[yihui]

The code looks good. We just need an example: #265 (review) Thank you!

[yihui]

Thanks!