Gwrappy

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* Added gwrappy.compute for Google Compute Engine.
* Minor Bugfixes:
* drive.DriveUtility.list_files(): Removed fields, added orderBy and filter_exp.
* bigquery.utils.JobResponse: time_taken in __repr__ for some job types fixed.

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* Added more utilities
* utils.month_range: Chunk dates into months.
* utils.simple_mail: Send basic emails for alerts or testing. *Note*: For greater security and flexibility, do still use the gmail functionality within this package.
* utils.StringLogger: Simply wrapper for logging with a string handler and convenience functions for retrieving logs as a string.
* Added dateutil as a dependency

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* list methods now return a generator for memory efficiency
* BigQuery:
* list_jobs takes 2 new args *projection* and *earliest_date*
* Documentation updates

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* gwrappy.errors no longer imports service specific error objects. To access JobError, import it from gwrappy.bigquery.errors
* simple date range generator function added to gwrappy.utils

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* BigQuery:
* JobResponse now only sets time_taken if data is available.
* Fixed bug that raised KeyError when wait_finish=False, since endTime was unavailable in the API response.
* poll_resp_list returns JobReponse objects. Also propagates 'description' attribute if available.

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* Bug Fixes
* Documentation updates