Added add_headers() method to request objects

[DarkWiiPlayer]

Why?

Because sometimes you may want to set headers progressively instead of just having one long header table at the end of your code. Specially useful when setting defaults in before-filters (UTF-8, spoofing the server, adding a lapis version header, etc.)

How?

By just adding a simple method that calls the add_header method of the response object (see code)

Example

app:before_filter(function(self)	
	self:add_headers {
		content_type = "text/html; charset=utf-8";
		lapis_version = require "lapis.version";
		server = "Super Secret, even if you knew you wouldn't find any vulnerabilities on google!"
	}
end)

I also couldn't resist removing a line of code that did absolutely nothing (again, see code)

[DarkWiiPlayer]

I have no idea why that was a : instead of a =, but it is fixed now (I've said this before, but I don't moonscript)

[DarkWiiPlayer]

This mistake is probably a side-effect of writing too much CSS during the days leading up to this commit

[DarkWiiPlayer]

@leafo I just remembered this pull request and noticed it's still open. Am I supposed to do something more, like a feature request ticked?