Metlog-py

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- Properly handle 'self' arguments when decorators are used on a method.
- Only apply string formatting to 'oldstyle' messages if string formatting args
are actually provided.

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- Added a testcase against the UDP input plugin.
- Fixed bug in socket.sendto function signature.

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- MetlogClient's `override` argument now accepts method name to override
instead of `True`.
- Decorator tests now get the expected envelope version from the module source
code rather than hard coded in the tests.
- Added udp sender.

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- Plugin method names are now expected to be stored in the `metlog_name`
attribute of the provided function rather than passed in separately.
- 'oldstyle' messages now support string substitution using provided args and
the `exc_info` keyword argument for slightly better stdlib logging
compatibility.
- ZeroMQ sender now uses gevent safe implementations of `Queue` class and `zmq`
module if the gevent monkeypatches have been applied.

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- Added `StdLibLoggingSender` that delegates message delivery to Python's
standard library `logging` module.

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- Refactored / simplified filter and plug-in config loading code
- Filter functions now use closures for filter config (matching plug-in config)
instead of passing the config as an argument each time.
- `MetlogClient.add_method` now supports `override` argument to force the issue
of replacing existing attributes.
- Added `metlog_hostname` and `metlog_pid` to the message envelope handed to the
sender.
- Added support for `rate` argument to `MetlogClient.incr` method.
- `MetlogClient.timer` converted from a property to a method, allowing for much
better performance and much simpler code.
- Got rid of `new_default` argument `MetlogClientHolder.delete_client`. Folks
can set a new default w/ another function call if necessary.
- `DebugCaptureSender.__init__` now accepts arbitrary keyword args and stores
them as attributes on the instance to allow for easier testing of the config
parsing code.