split CONTRIBUTING.md from README.md
add "Git Flow" link to CONTRIBUTING.md
Clean up acts_as_journalized SaveHooks
acts_as_journalized: Use save! instead of save

This should prevent journals silently not being saved on validations
errors.
JournalManager: Fix attempting to create two journals with same version

Calculate journal version based on existing maximum instead of count.

Up to now, when removing a journal note with another journal entry
existing afterwards, there could be a single journal with version 2,
resulting in validation errors for the next attempt to add a journal.
Fix WikiController test_update_stale_page_should_not_raise_an_error

The test didn't specify the version it depended on, so its assertion failed.

I have no idea why the second changed assertion ever worked, since the
journal's version should never change. This restores the line as it
was before commit c25bbee177dbb71d983ff78ab528889a6ba4bec5.
Merge branch 'fix/wp_journal_not_added' into release/3.0
Mark API v1 as deprecated in CHANGELOG
Merge pull request #1176 from marutosi/finn-contribute

split CONTRIBUTING.md from README.md
Merge pull request #1177 from marutosi/finn-branch-model

add "Git Flow" link to CONTRIBUTING.md
Fix travis' ruby version

Because of RVM not supporting Ruby 2.1.0 anymore we need to change the
Ruby version for travis.
Add patch to fix Rails' hash types with Ruby 2.1.1

Might also help us with Ruby 2.2 until we have Rails 4.