* Added changelog.

* Added PR template note.

* Update .github/PULL_REQUEST_TEMPLATE.md

Co-Authored-By: nventuro <nicolas.venturo@gmail.com>

* Update PULL_REQUEST_TEMPLATE.md

* Update CHANGELOG.md

Co-Authored-By: nventuro <nicolas.venturo@gmail.com>

* Update CHANGELOG.md

Co-Authored-By: nventuro <nicolas.venturo@gmail.com>

* Apply suggestions from code review

Co-Authored-By: nventuro <nicolas.venturo@gmail.com>

* Added more headers and sub-headers.

* Added deprecations category.

* Added PR links.

* Added PausableCrowdsale.

* Addressed review comments.

* Update CHANGELOG.md

Co-Authored-By: nventuro <nicolas.venturo@gmail.com>