Release Name: 0.40

Notes:



Changes:
*  Add `"Header-ID-Type:"` header.
If its value is 'escape', automatic generated header ID varies.
	
    Header-ID-Type: escape
			
* Add new syntax sugar for anchor link. Following links are both equal. 
	
    [TargetHeader](#)
    [TargetHeader](#TargetHeader)
	
* 'shift_jis' is enabled for encoding specification.

* Fix problems
	
	* On ruby 1.9.x, error raises if specified encoding is 'shift-jis'.