---------------
- API CHANGE: modified pyproject.toml to require Python version
3.6.8 or later for pyparsing 3.x. Earlier minor versions of 3.6
fail in evaluating the `version_info` class (implemented using
`typing.NamedTuple`). If you are using an earlier version of Python
3.6, you will need to use pyparsing 2.4.7.

- Improved pyparsing import time by deferring regex pattern compiles.
PR submitted by Anthony Sottile to fix issue 362, thanks!

- Updated build to use flit, PR by Michał Górny, added BUILDING.md
doc and removed old Windows build scripts - nice cleanup work!

- More type-hinting added for all arithmetic and logical operator
methods in `ParserElement`. PR from Kazantcev Andrey, thank you.

- Fixed `infix_notation`'s definitions of `lpar` and `rpar`, to accept
parse expressions such that they do not get suppressed in the parsed
results. PR submitted by Philippe Prados, nice work.

- Fixed bug in railroad diagramming with expressions containing `Combine`
elements. Reported by Jeremy White, thanks!

- Added `show_groups` argument to `create_diagram` to highlight grouped
elements with an unlabeled bounding box.

- Added `unicode_denormalizer.py` to the examples as a demonstration
of how Python's interpreter will accept Unicode characters in
identifiers, but normalizes them back to ASCII so that identifiers
`print` and `𝕡𝓻ᵢ𝓃𝘁` and `𝖕𝒓𝗂𝑛ᵗ` are all equivalent.

- Removed imports of deprecated `sre_constants` module for catching
exceptions when compiling regular expressions. PR submitted by
Serhiy Storchaka, thank you.