Ddtrace

**Major changes**
- added`msgpack-python` as a dependency
- using Trace Agent API `v0.3` that supports both JSON and Msgpack formats
- provided `JSONEncoder` and `MsgpackEncoder` that are switched at runtime the API `v0.3` is not reachable (`404`)
- `MsgpackEncoder` is the current default encoder
- `MsgpackEncoder` will not be used if the pure Python implementation is used

**Documentation**
- added [ElasticSearch docs](http://pypi.datadoghq.com/trace/docs/#module-ddtrace.contrib.elasticsearch)

Read the [full changeset](https://github.com/DataDog/dd-trace-py/compare/v0.4.0...v0.5.0)

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0.4.0 is a "major" release of the `dd-trace-py`. Please test thoroughly on staging before rolling out to your production clusters.

Enhancements
- automatically patch contrib libraries with `from ddtrace import monkey; monkey.patch_all()`. A few notes:
- The previous ways of patching still exist, but are deprecated and might be no-ops. They will be removed in a future version.
- When you add `patch_all` remove your old instrumentation code.
- Web frameworks still require middleware.
- experimental support for (much faster) msgpack serialization. disabled by default. will be enabled in a future release.

Integrations
- add integration for the [Bottle](web framework) web framework. (see 86)

Bug Fixes
- correctly trace django without auth middleware (see 116)



Read the [full changeset](https://github.com/DataDog/dd-trace-py/compare/v0.3.16...v0.4.0).

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Bugfixes
- Handle memory leaks when tracing happens in a forked process (Issue 84)
- Fix error code in spans from the request library (thanks brettlangdon)
- Better handling of unicode tags (thanks brettlangdon)
- Allow easy configuration of host & port in the Django integration.

Enhancements
- Cap the number of traces buffered in memory.
- Higher trace submission throughput.
- Preliminary work on gevent support. Not fully complete.

Read the [full changeset](https://github.com/DataDog/dd-trace-py/compare/v0.3.15...v0.3.16)

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Integrations
- add tracing for the requests library

Read the [full changeset](https://github.com/DataDog/dd-trace-py/compare/v0.3.14...v0.3.15)

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Integrations
- [pylons] allow users to set resources inside handlers
- [django] add support for the Django cache framework

Enhancements
- add a trace sampler so that users can discard spans using a `RateSampler` (more info: http://pypi.datadoghq.com/trace/docs/#sampling)

Read the [full changeset](https://github.com/DataDog/dd-trace-py/compare/v0.3.13...v0.3.14)

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New integrations
- added `pylibmc` Memcached client integration
- improved Django integration providing a Django app that instrument Django internals

Read the full [changeset](https://github.com/DataDog/dd-trace-py/compare/v0.3.12...v0.3.13)

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