Release Name: 0.21

Notes:



Changes:
* Alter bluefeather command output.
	
  * If you specify -v (--verbose), bluefeather show encoding of each file at converting.
		
  * If you specify --version, bluefeather also show release date of this version.
	
* Fix fenced code block bug that last line on 2-or-more lines block is wrongly converted. For example, `#` symbol or `:` symbol.
	
* Fix bug that a document encoded by UTF-8 with BOM can't be correctly converted.