Remove old release notes as the maintenance policy has changed.

[satoryu]

Old documents sometimes make developers and users confusing like #123 . If the maintainer made a decision they will never provide release notes under doc/release_notes and provide History.rdoc instead, the old release notes should be removed.

CC: @hsbt @AknEp

[drbrain]

We can't remove old release notes because it makes it harder to find when a bug was introduced.

Merging old-style release notes into History.rdoc would be OK.

[zzak]

As an alternative, we could put a README in this directory which explains the current policy for release notes.

[hsbt]

I want to merge doc/release_notes and History.rdoc. After that I will merge this pull request.

[satoryu]

Thank you for your replies.

@drbrain @hsbt ok, give me time to merge the old release notes into History.rdoc.

@zzak good idea it would work! btw, I don't know the current policy the maintainers made. Can I hand over it to the maintainers?

[satoryu]

I've merged all release notes into History.rdoc (as I removed some part such as What is Rake) and put README.md in the directory doc/release_notes to tell visitors they should see History.rdoc.

omg, failed...
Do you have any idea to fix it?

[hsbt]

I invoke failing test again. It works.

[satoryu]

Please have a look through the PR again when you have time. @zzak @drbrain

[hsbt]

@satoryu Thank you for your work!