Allow using {}, [] and <> for function surround

[miseran]

With this patch, if a function name ends in the character "[", "{" or "<", that is used as the delimiter instead of "(".

The main use case for me is in LaTeX, where functions use the "{" delimiters. For example, ysiwf\textbf{<CR> to make a word bold. I think this may be useful in other situations as well, for example array indexing.

[tommcdo]

:+1: Nicely done!

[Hotschke]

:+1:

Currently I have defined let b:surround_{char2nr("c")} = "\\\1command: \1{\r}". Since dot-repeating of ysgnctextbf<CR> does not work , it's possible to use ysgnf\textbf{ and dot repeat it.