Don’t mess with hl()+contents

What does hl() mean? It looks like “highlight an empty string”, but is actually 
“reset highlight style”. In addition if you are writing “hl()” function for new 
renderer you need to care about “contents” variable (in two places!: None for 
super() call and (contents or u'') after super() call) though function is 
actually doing nothing with it. It is just inconvenient.
Use escape_hl_* variables for prompts deriving from ShellRenderer

This is faster then super() calls and also more convenient.
Fixes #142 just as well
Added auto_rewrite method to pre_0_11

It raises error without this
Merge branch 'ipython-fix' into local-develop
Merge branch 'shell-escape_hl' into local-develop
Merge branch 'hlstyle' into local-develop