v1.2.0

Contributor-facing changes

• Added templates for issues and pull requests -- by @Polandia94. (#78, #86)
• Updated the security policy with private vulnerability reporting options through GitHub, the project maintainer, and aio-libs -- by @tarasko. (#79)

Miscellaneous internal changes

• Refactored transport hierarchy, prepared code for proactor transports -- by @tarasko. (#74)
• Converted aiofastnet logo into svg, adjusted colors to make it contrast both for light and dark themes -- by @tarasko. (#91)
• Set up Towncrier for managing release notes -- by @tarasko. (#95)