MySQL, PostgreSQL, and SQL adapter packages is moved to it's own repositories

[Fs02]

Hi,

Adapters packages has been refactored and extracted to it's own repositories, please find it here:

• https://github.com/go-rel/mysql
• https://github.com/go-rel/postgres
• https://github.com/go-rel/sqlite3

Existing adapter packages under github.com/go-rel/adapter/[db] is now deprecated and maybe removed later.

Thank you