This adds prompt_toolkit based shell in addition to existing readline
shell. By default regular readline shell is loaded, to use
prompt_toolkit version you need to add:
$PROMPT_TOOLKIT_SHELL = True
to your ~/.xonshrc
Another nice thing to add there is:
from xonsh.pyghooks import XonshLexer
$HIGHLIGHTING_LEXER = XonshLexer
that adds highlighting of shell input (may be a bit annoying sometimes).
There is no key for inserting indentation yet, it will be improved in the
future.
