* improve KeyBuilder documentation

* clarify slightly

* Tweak docs, add types

---------

Co-authored-by: Andreas Kloeckner <inform@tiker.net>

* add visualize_graph

* add package

* replace graphviz

* lint fixes

* small style fixes

* fix exception text

* restructure

* add a small test

* skip test if dot not available

* further restructure, rename to get_graph_dot_code

* remove useless assert

* small doc fix

* change Iterable to Collection

* flake8

* fix log message

* explicit return in non-svg case

* make sure that nodes not in graph.keys() appear in output

* rename dot.py -> graphviz.py

* add foldmethod

* add edge_labels

* fix doc

* trigger GitHub actions

* bump CI again

* rename to as_graphviz_dot and add noed_labels

* remove explicit edges storage

* test node_labels explicitly

* flake8

* graph: create GraphT

* shorten type display

* re-add 'graph' in arg list

* fix is_connected

* minor doc fixes

* another is_connected fix

* make NodeT bound to Hashable

* a few more type simplifications

* make NodeT a TypeAlias too

* add NodeT to aliases in docs

* add return type doc to is_connected

* remove GraphT from arg doc

* change to full name

* add pytest_raises_on_rank

* better type annotation

* add copyright to mpi.py

* add test_mpi.py

* fix doc

* Clarify test

https://github.com/inducer/modepy/pull/38#issuecomment-846472970

This change takes common code generation functionality out of
pytools.py_codegen and makes it a separate module.

A language-independent parent class of PythonCodeGenerator is also
added.

The version is bumped to 2020.4