MNT: Use SPDX license expression

[matthewfeickert]

• Use the recommended SPDX license expression string for the license identifier.
  • c.f. https://packaging.python.org/en/latest/guides/writing-pyproject-toml/#license
• Remove the trove classifier as well, given DeprecationWarning.

********************************************************************************
Please consider removing the following classifiers in favor of a SPDX license expression:
License :: OSI Approved :: GNU Lesser General Public License v2 or later (LGPLv2+)
See https://packaging.python.org/en/latest/guides/writing-pyproject-toml/#license for details.
********************************************************************************

• Additionally add long_description_content_type to pass 'twine check --strict'.

[matthewfeickert]

@tacaswell This addresses some metadata issues for getting cibuildwheel passing.

[matthewfeickert]

Given

datrie/COPYING

Lines 1 to 2 in c9525da

	GNU LESSER GENERAL PUBLIC LICENSE
	Version 2.1, February 1999

and the existing

datrie/setup.py

Line 22 in c9525da

'License :: OSI Approved :: GNU Lesser General Public License v2 or later (LGPLv2+)',

the SPDX identifier should be for v2.1+.

[tacaswell]

This is mechanical "spell checking" of the license meta-data, but I would like to give @kmike and @superbobry a chance to weigh in before we merge this.

[matthewfeickert]

This is mechanical "spell checking" of the license meta-data, but I would like to give @kmike and @superbobry a chance to weigh in before we merge this.

👋 Ping @kmike @superbobry

[matthewfeickert]

@tacaswell Do you have alternative ways of contacting them?