'PreviewSignature' does not work correctly with 'bang'

[chengzeyi]

In README.md, it was introduced:

Preview the function signature circularly in the command line:

PreviewSignature[!] [function name]
If the function name is not provided, current word under cursor will be taken as function name. 
If bang ! sign is given, the nearest function name to the cursor position is chosen.

But in the script, it was written:

function! s:PreviewSignature(bang, ...)
	let funcname = (a:0 > 0)? a:1 : ""
	if a:bang 
		let funcname = '<?>'
	endif
	call preview#function_echo(funcname, 0)
endfunc

Seems that with a bang given, the first argument passed to preview#function_echo() will be '<?>'. And preview#function_echo() is just a simple wrapper around preview#function_define() by passing its first parameter to it. But when I digged a little deeper into that function, I noticed the following lines, which a:name is indeed funcname occurring above:

if a:name == ''
	let name = preview#function_guess(line[0:endpos])
elseif a:name == '<?>'
	let name = expand('<cword>')
else
	let name = a:name
endif

Surprisingly, if a;name is '<?>', which is the circumstance we expect to have a 'guess' about the nearest function name by giving a bang adhering the 'PreviewSignature' command, what the function does is only picking the word under the cursor. However without a bang, an inner function called preview#function_guess() would try to guess the nearest function name. The command just behave conversely against the documentation.

[chengzeyi]

I suggest the easiest way to solve this problem is to correct README.md, while modification of the source code itself is not necessary :-)