[ANN] ruby-oci8 2.2.1

Ruby-oci8 2.2.1 is released. This is the Oracle module using OCI8 API.

   http://www.rubydoc.info/github/kubo/ruby-oci8

New Features

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### Add OCI8::Metadata::Boolean

Support boolean type binding. This feature requires Oracle 12c client
and server.
This doesn't work when either Oracle server or client is 11g or lower.

Fixed Issues
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The following two issues were introduced in ruby-oci8 2.2.0.

### Fix handle leaks in OCI8#ping

This bug affects Oracle 10gR1 client only.

### Fix potential segmentation fault on ruby process termination

Other Changes
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- Reduce compilation time by dropping unnecessary checks.

- Delete unused code which was added to support old Oracle and ruby 1.8.