0.6.2.3

Security

• disable RSA PKCS 1.5 by default (#22); thanks @thalman

Other

• avoid using empty prototypes; support Clang 15 and XCode 14.3
• build shared library on Cygwin by adding -no-undefined to LDFLAGS (#20); thanks @fd00
• reformat using clang-format-18.1.3
• regenerate autoconf files using autoconf 2.72
• update github actions to avoid warnings