support cygwin x86_64.
Fix tests in an environment where the data size of "CAST('1' AS CHAR(1 char))" is wrong.
Suppress warnings "MiniTest::Unit::TestCase is now Minitest::Test" when minitest gem is installed.
Fix OCI8::Metadata::Synonym#schema_name and #translated_name for synonyms with a database link and without schema_name.
Fix for Windows x64. OCI.lib for MSVC doesn't work with mingw64 compilers.
Fix URL in the error message.
Update the version to 2.1.6.