Add 'jupyter kernel' command

A simple lead in to the 'kernel nanny' work, this adds a command so you
can do:
jupyter kernel --kernel python

jupyter_client/kernelapp.py

@@ -0,0 +1,66 @@
+import os
+import signal
+import uuid
+
+from jupyter_core.application import JupyterApp
+from tornado.ioloop import IOLoop
+from traitlets import Unicode
+
+from . import __version__
+from .kernelspec import KernelSpecManager
+from .manager import KernelManager
+
+class KernelApp(JupyterApp):
+    version = __version__
+    description = "Run a kernel locally"
+
+    classes = [KernelManager, KernelSpecManager]
+
+    aliases = {
+        'kernel': 'KernelApp.kernel_name',
+        'ip': 'KernelManager.ip',
+    }
+
+    kernel_name = Unicode(
+        help = 'The name of a kernel to start'
+    ).tag(config=True)
+
+    def initialize(self, argv=None):
+        super(KernelApp, self).initialize(argv)
+        self.km = KernelManager(kernel_name=self.kernel_name,
+                                config=self.config)
+        cf_basename = 'kernel-%s.json' % uuid.uuid4()
+        self.km.connection_file = os.path.join(self.runtime_dir, cf_basename)
+        self.loop = IOLoop.current()
+
+    def setup_signals(self):
+        if os.name == 'nt':
+            return
+
+        def shutdown_handler(signo, frame):
+            self.loop.add_callback_from_signal(self.shutdown, signo)
+        for sig in [signal.SIGTERM, signal.SIGINT]:
+            signal.signal(sig, shutdown_handler)
+
+    def shutdown(self, signo):
+        self.log.info('Shutting down on signal %d' % signo)
+        self.km.shutdown_kernel()
+        self.loop.stop()
+
+    def log_connection_info(self):
+        cf = self.km.connection_file
+        self.log.info('Connection file: %s', cf)
+        self.log.info("To connect a client: --existing %s", os.path.basename(cf))
+
+    def start(self):
+        self.log.info('Starting kernel %r', self.kernel_name)
+        try:
+            self.km.start_kernel()
+            self.log_connection_info()
+            self.setup_signals()
+            self.loop.start()
+        finally:
+            self.km.cleanup()
+
+
+main = KernelApp.launch_instance

scripts/jupyter-kernel

@@ -0,0 +1,5 @@
+#!/usr/bin/env python
+from jupyter_client.kernelapp import main
+
+if __name__ == '__main__':
+    main()

setup.py

@@ -91,6 +91,7 @@
         'console_scripts': [
             'jupyter-kernelspec = jupyter_client.kernelspecapp:KernelSpecApp.launch_instance',
             'jupyter-run = jupyter_client.runapp:RunApp.launch_instance',
+            'jupyter-kernel = jupyter_client.kernelapp:main',
         ]
     }
     setup_args.pop('scripts', None)