more aggressive wildcards

[karlseguin]

I noticed that a route of:

r:match('GET', '*', ...)

doesn't match

'GET', '/'

Or, more globally, it doesn't match zero-elements.

I changed match_one_path and added the if block within the for:

local function match_one_path(node, path, f)
  for token in path:gmatch("[^/.]+") do
    node[token] = node[token] or {}
    if token == '*' and not node['LEAF'] then
      node['LEAF'] = f
    end
    node = node[token]
  end
  node["LEAF"] = f
end

All tests pass, but I'm loath to open a PR as this would probably break someone's expectations.