[FR] Support missing events (#76)

[FR] Add support for sample base queries in elasticsearch (#74)

[Bug] Support runs count on first query (#73)

Add support for array variable type validation (#71)

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Co-authored-by: Mika Ayenson <mika.ayenson@elastic.co>

[Bug] Fix as keyword and as ecs field overlap bug (#67)

Add support for sequence alias (#65)

Update version to 0.9.13 for release (#63)

Add support for optional fields behind Elasticsearch flag (#59)

* Add support for optional fields behind Elasticsearch flag
* Pick different PyYAML versions depending on python version
* Remove unnecessary lexer rule priority
* Update syntax message
* Shrink error message because of E501

Add support for unicode escape sequences per spec (#56)

* Add support for unicode escape sequences per spec
* Add tests for unicode parsing
* Pin pluggy for python 2.7 tests

Add $variable syntax behind parser endpoint flag (#55)

* Add $variable syntax behind parser endpoint flag
* Remove python 3.6 from matrix
* Tighten the pytest dependency
* Pin the version of contextlib2 transitive dependency
* Fix contextlib litera
* Fix grammar for NAME syntax and add another test
* Turn on full tracebacks in the parser
* Remove fail-fast strategy
* Close function calls with )
* Fix schema bugs
* Update parser and AST handling of variables
* Add comments for things behind the parser flag
* Update release date
* Fix docstring