Bind additional error codes (#125) * Fix errors.ml generator and bind missing CURLE_OBSOLETE (code 50) The generator's index/value safety check wasn't working as it relied on the preprocessor evaluating enum constants, which are always zero. Switch to static assertions at file scope that compiler can validate. * Bind CURLE_* codes 82-101 added in libcurl 7.19.0..8.8.0 Add the 20 error variants upstream introduced since CURLE_AGAIN. These previously surfaced as exceptions with no matching variant and generic "Unknown Error" string. Minimum supported libcurl stays at 7.28.0. * Add changelog entry for new error code additions * Add executable stanza for errors.ml