Add send voice message.

fix https://github.com/xhzengAIB/MessageDisplayKit/issues/7
delete png files.
Update README.md
Merge pull request #14 from Aevit/master

fix infinite loop when change textview height for iOS6
fix memory bug
Fix the copyZone method
fix the bug from iOS7

1、fix the send button's enable state after sended text for iOS7
2、rename to voice
Update README.md
Update README.md
Update README.md
Update README.md
Update README.md
Merge branch 'master' of https://github.com/xhzengAIB/MessageDisplayKit into XH-master

# By Jack
# Via Jack
* 'master' of https://github.com/xhzengAIB/MessageDisplayKit:
  Update README.md
  Update README.md
  Update README.md
  Update README.md
  Update README.md
  fix the bug from iOS7
  Fix the copyZone method
  fix memory bug
  Update README.md
  delete png files.
  Add send voice message.

Conflicts:
	Example/MessageDisplayExample/MessageDisplayExample/XHDemoWeChatMessageTableViewController.m
	MessageDisplayKit/Classes/Controllers/XHMessageTableViewController.h
	MessageDisplayKit/Classes/Controllers/XHMessageTableViewController.m
Merge branch 'XH-master'

# By Jack
# Via Jack (2) and Aevit (1)
* XH-master:
  Update README.md
  Update README.md
  Update README.md
  Update README.md
  Update README.md
  fix the bug from iOS7
  Fix the copyZone method
  fix memory bug
  Update README.md
  delete png files.
  Add send voice message.

Conflicts:
	Example/MessageDisplayExample/MessageDisplayExample/XHDemoWeChatMessageTableViewController.m
	MessageDisplayKit/Classes/Controllers/XHMessageTableViewController.h
	MessageDisplayKit/Classes/Controllers/XHMessageTableViewController.m