Great-expectations

* BREAKING: slack webhook URL now must be in the profiles.yml file (treat as a secret)
* Profiler improvements:
- Display candidate profiling data assets in alphabetical order
- Add columns to the expectation_suite meta during profiling to support human-readable description information
* Improve handling of optional dependencies during CLI init
* Improve documentation for create_expectations notebook
* Fix several anachronistic documentation and docstring phrases (659, 660, 668, 681; thanks StevenMMortimer)
* Fix data docs rendering issues:
- documentation rendering failure from unrecognized profiled column type (679; thanks dinedal))
- PY2 failure on encountering unicode (676)

* Standardize the way that plugin module loading works. DataContext will begin to use the new-style class and plugin identification moving forward; yml configs should specify class_name and module_name (with module_name optional for GE types). For now, it is possible to use the "type" parameter in configuration (as before).
* Add support for custom data_asset_type to all datasources
* Add support for strict_min and strict_max to inequality-based expectations to allow strict inequality checks
(thanks RoyalTS!)
* Add support for reader_method = "delta" to SparkDFDatasource
* Fix databricks generator (thanks sspitz3!)
* Improve performance of DataContext loading by moving optional import
* Fix several memory and performance issues in SparkDFDataset.
- Use only distinct value count instead of bringing values to driver
- Migrate away from UDF for set membership, nullity, and regex expectations
* Fix several UI issues in the data_documentation
- Move prescriptive dataset expectations to Overview section
- Fix broken link on Home breadcrumb
- Scroll follows navigation properly
- Improved flow for long items in value_set
- Improved testing for ValidationRenderer
- Clarify dependencies introduced in documentation sites
- Improve testing and documentation for site_builder, including run_id filter
- Fix missing header in Index page and cut-off tooltip
- Add run_id to path for validation files

* New Validation Renderer! Supports turning validation results into HTML and displays differences between the expected and the observed attributes of a dataset.
* Data Documentation sites are now fully configurable; a data context can be configured to generate multiple
sites built with different GE objects to support a variety of data documentation use cases. See data documentation guide for more detail.
* CLI now has a new top-level command, `build-documentation` that can support rendering documentation for specified sites and even named data assets in a specific site.
* Introduced DotDict and LooselyTypedDotDict classes that allow to enforce typing of dictionaries.
* Bug fixes: improved internal logic of rendering data documentation, slack notification, and CLI profile command when datasource argument was not provided.

* Fix missing requirement for pypandoc brought in from markdown support for notes rendering.

* Fix numerous rendering bugs and formatting issues for rendering documentation.
* Add support for pandas extension dtypes in pandas backend of expect_column_values_to_be_of_type and expect_column_values_to_be_in_type_list and fix bug affecting some dtype-based checks.
* Add datetime and boolean column-type detection in BasicDatasetProfiler.
* Improve BasicDatasetProfiler performance by disabling interactive evaluation when output of expectation is not immediately used for determining next expectations in profile.
* Add support for rendering expectation_suite and expectation_level notes from meta in docs.
* Fix minor formatting issue in readthedocs documentation.

* BREAKING: Harmonize expect_column_values_to_be_of_type and expect_column_values_to_be_in_type_list semantics in
Pandas with other backends, including support for None type and type_list parameters to support profiling.
*These type expectations now rely exclusively on native python or numpy type names.*
* Add configurable support for Custom DataAsset modules to DataContext
* Improve support for setting and inheriting custom data_asset_type names
* Add tooltips with expectations backing data elements to rendered documentation
* Allow better selective disabling of tests (thanks RoyalITS)
* Fix documentation build errors causing missing code blocks on readthedocs
* Update the parameter naming system in DataContext to reflect data_asset_name *and* expectation_suite_name
* Change scary warning about discarding expectations to be clearer, less scary, and only in log
* Improve profiler support for boolean types, value_counts, and type detection
* Allow user to specify data_assets to profile via CLI
* Support CLI rendering of expectation_suite and EVR-based documentation