Radical.utils

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- remove a high-requency debug message

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- fix registry key insertion on path overwrite

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- bump python test env to 3.7
- cfg update
- default value for debug level
- fixed error related to default value `None`
- fix sphinx errors / warnings
- format fix
- lint the linter
- make logger debug level inspectable
- newer sphinx
- recover `logging.Logger` inheritance
- speed up logger
- switch to requirements files to make RTD happy

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- fix shell quoting

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- add zmq pipe implementation

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- doc strings
- fix double subscription on Subscribers which hold global zmq sockets
- fix pubsub logging, consistent variable names, shorter timeout
- fix `ratio` interpretation for bisect
- make bridge silent by default
- simpler server address inspection