Correct cross-platform venv path handling (beeware#310)

Corrects for changes in Python 3.14's handling of sysconfig._init_config_vars(),
ensuring that cross-platform virtual environments have correct include paths.

Merge recent changes from main. (beeware#311)

Includes adding a cross-env ci check, and converting the README to markdown.

Correct handling of sysconfig._BASE_PREFIX in cross environments. (be…

…eware#297)

Ensure that sysconfig._BASE_PREFIX is bound to base_prefix, not prefix.

Correct handling of sysconfig._BASE_PREFIX in cross environments. (be…

…eware#298)

Ensure that sysconfig._BASE_PREFIX is bound to base_prefix, not prefix.

Correct issues with testing in CI (beeware#295)

Adds a patch to account for empty testing simulator sets.

Also adds CI to confirm the testbed works in a CI environment.

Correct issues with testing in CI (beeware#296)

Adds a patch to account for empty testing simulator sets.

Also adds CI to confirm the testbed works in a CI environment.

Temporarily disable dSYM production. (beeware#293)

Temporarily disable dSYM production (beeware#294)

Add missing modulemap base files.

Add missing modulemap base files.