Added better support for generic type subclass analysis, including support for covariance and contra variance.
Fixed bug that caused type analysis not to converge sometimes, resulting in an infinite loop.
Fixed crashing bug that could occur if typeshed files were not found.
In VS Code extension, filled in "source" string so "pyright" appears in the problems panel.
Added support for a few configuration settings in VS Code that are common to the standard VS Code Python extension.
Added new config setting "reportMissingTypeStubs" to differentiate from "reportMissingImports".
Fixed bug in "isinstance" type constraint handling. Its logic was reversed when checking for subtypes.
Disabled reporting of errors to return type mismatches in generator functions. This will be enabled again once generator and coroutine support is added to the analyzer.
Added an error output when configuration specifies a python version older than 3.0.
Fixed reported type analysis bug that affected built-in types that had aliases defined in the collections.pyi type stub (notably, Deque, DefaultDict and ChainMap).