CHANGELOG translate into Japanese

from 7382a6e6a66d3f80da955ebbcd82250f99321900 and 233489ddfe4698b24dfcdc1daf3ca15bc880e4b1
Merge pull request #933 from ykzts/changelog-translate-ja-7382a6e6a66d3f80da955ebbcd82250f99321900-and-233489ddfe4698b24dfcdc1daf3ca15bc880e4b1

CHANGELOG translate into Japanese
Rephrase a couple of items.
Fix some grammos and remove trailing spaces.
Add missing translation for the changes in 1.5.1.
Add missing translation for these as well.
Add MIT license to gemspec (closes #938)
fix undefine method error when running rake tasks
Merge pull request #946 from eitoball/fix_rakefile_error

Fix "undefined method `licenses='"  when running rake tasks
Add ruby-2.0.0 and allow ruby-head to fail
Add ruby 2.0.0 and drop ruby 1.9.2.
Library paths must be prepended to $LIBPATH to give the highest priority.
Fix iconv prefix detection.

- Make preserving_globals *actually* preserve the original values.

- Prepend parameters rather than appending them.
Refactor MiniPortile object generation.
Add an option --use-system-libraries and show some build information.
Update the copyright notice, adding my name.
Merge pull request #947 from eitoball/add_2_0_0_and_allow_ruby_head_to_fail

Add ruby-2.0.0 and allow ruby-head to fail to Travis CI config
Mention --use-system-libraries.