Install xonsh via pip

Author: simon04

setup.py

@@ -106,6 +106,7 @@ def main():
             'docopt>=0.6.2,<1.0.0',
             'github3.py>=1.0.0a1',
             'html2text>=3.200',
+            'xonsh>=0.2.2',
         ],
         skw['entry_points'] = {
             'pygments.lexers': ['gitsome = xonsh.pyghooks:XonshLexer',