feat: move solidity-docgen to a general folder and compact repository config files

[0xneves]

Feature Request

Describe the Feature Request

Organize the documentation and configurations of the repository.

Describe Preferred Solution

Create solidity-docgen folder inside docs Change the output of solidity-docgen into docs/solidity-docgen Move the following into the docs folder:

• CODE_OF_CONDUCT.md
• CONTRIBUTING.md
• SECURITY.md