[ANN] ruby-oci8 2.2.0

Ruby-oci8 2.2.0 is released. This is the Oracle module using OCI8 API.

  http://rubyforge.org/projects/ruby-oci8/

Ruby 1.8 support was dropped. Use ruby-oci8 2.1.8 for ruby 1.8.
Oracle 9i support was dropped. Use ruby-oci8 2.1.8 for Oracle 9i.

New Features

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### Support LOB over 4G

### Fix to install ruby-oci8 on OS X 10.11 El Capitan.

`DYLD_LIBRARY_PATH` is unset for security reasons on OS X 10.11.
The installtion script was changed to work without `DYLD_LIBRARY_PATH`
and check the environment variable `OCI_DIR` also to tell instant
client directory.

Other Changes
-------------

- Change the default prefetch row size to 100.

- Add notice that OCI8::LOB is an I/O object and is closed
    when a associating connection is closed.

- Add ruby-oci8 version the driver name, which is displayed in
    `V$SESSION_CONNECT_INFO.CLIENT_DRIVER` for Oracle 12.1.0.2 or later.
    (suggested by Christopher Jones)

- Use `Kernel.load` in ruby-oci8.gemspec instead of `load`.
    `load`, without the module name, is used as `Gem::Specification.load`
    by some ruby installations.

- Add OCI8.charset_name2id and OCI8.charset_id2name.
    Mark OCI8#charset_name2id and OCI8#charset_id2name as deprecated.