Customizations with prompts not repeatable with `.`

[MarcelRobitaille]

This is related to #106.

For example, I want to have something similar to the built in function surroundings but for LaTeX macros:

let g:surround_{char2nr('l')} = "\\\1LaTeX macro\1{\r}"

When I press . to repeat it, I am prompted for the name again.

I have confirmed that . with the built in function surrounding works as expected (I am not prompted for the function name again).

Is this intended behaviour?