Undestroy method for paranoid models
Return failure from undestroy before hooks execute
Fix test data typo
Promisify tests
Remove superfluous .then
Rename undestroy to restore
Better tests
Fix test typo
keep original error message when wrapping in DatabaseError

fixes #2521
Test fix
Update README.md
Allow removing has-many associations by id
Merge pull request #2563 from simong/has-many-remove-by-id

Allow removing has-many associations by id
Add support for 'IS NULL' comparison
Merge pull request #2565 from chainlink/equal-null

Add support for 'IS NULL' comparison
Merge pull request #2552 from defunctzombie/fix_error_message

keep original error message when wrapping in DatabaseError
Prefer index name when mapping unique constraint errors

When using migrations to create indexes instead of sync or when unique
index name has fields with underscores (was problem at least with
postgres implementation) then it was not possible to set custom error
message, because mapping the error thrown from database always failed.
Fixed by using indexName always for mapping the error if possible.
Update changelog
update/clean readme

- update some of the links
- change h3 to h2 for sections
- add disclaimer about runnable not being up-to-date
- change twitter link to @SequelizeJS instead of @sdepold
Merge pull request #2569 from vpontis/update-readme

update/clean readme