* Add new capability to the PEG parser to type variable assignments. For instance:
```
| a[asdl_stmt_seq*]=';'.small_stmt+ [';'] NEWLINE { a }
```
* Add new sequence types from the asdl definition (automatically generated)
* Make `asdl_seq` type a generic aliasing pointer type.
* Create a new `asdl_generic_seq` for the generic case using `void*`.
* The old `asdl_seq_GET`/`ast_seq_SET` macros now are typed.
* New `asdl_seq_GET_UNTYPED`/`ast_seq_SET_UNTYPED` macros for dealing with generic sequences.
* Changes all possible `asdl_seq` types to use specific versions everywhere.
This commit removes the old parser, the deprecated parser module, the old parser compatibility flags and environment variables and all associated support code and documentation.
* Remove the slice type.
* Make Slice a kind of the expr type instead of the slice type.
* Replace ExtSlice(slices) with Tuple(slices, Load()).
* Replace Index(value) with a value itself.
All non-terminal nodes in AST for expressions are now of the expr type.
The fix changes copy_location() to require an extra node from which to extract the end location, and fixing all 5 call sites.
https://bugs.python.org/issue39235
When parsing an "elif" node, lineno and col_offset of the node now point to the "elif" keyword and not to its condition, making it consistent with the "if" node.
https://bugs.python.org/issue39031
Automerge-Triggered-By: @pablogsal
