* Adding ICompletionExtension interface
* Adding extension loading and execution logic
* Fixing compilation error in VS 2017
* Using MEF for completion extension discovery
* using await on GetCompletionItems
* Adding an integration test for completion extension and update the completion extension interface
* Update the completion extension test
* Fix issues based on review comments
* Remove try/cache based on review comments, fix a integration test.
* More changes based on review comments
* Fixing SendResult logic for completion extension loading
* Only load completion extension from the assembly passed in, add more comments in the test
* Adding right assert messages in the test.
* More fixes based on review comments
* Dropping ICompletionExtensionProvider, load assembly only if it's loaded at the first time or updated since last load.
* Fix based on the latest review comments
* Adding missing TSQL functions in default completion list
* Update jsonrpc documentation for completion/extLoad
* fixed peek definition tokenizing
* fixed signature help test
* added new heuristic for PeekDefinition behaviour
* added tests for new heuristic
* fixed code according to Kevin's CR
* fixed failing test due to shared connection
* changed uri for procedure test
* DbColumn and ReliableConnection tests
* More retry connection tests
* More tests
* Fix broken peek definition integration tests
* Fix test bug
* Add a couple batch tests
* Add some more tests
* More tests for code coverage.
* Validation and Diagnostic tests
* A few more tests
* A few mote test changes.
* Update file path tests to run on Windows only
