Fix issues with Emacs 29 compatibility

[KarimAziev]

• use cl-lib instead of deprecated cl
• enable lexical bindings
• fix eieio issues
• rename dired-do-gist to gist-dired-do-gist
• remove overriding dired keymap
• fix all byte-compile warnings
• add more documentation strings

Important Note

New changes require merge request in gh.el to be merged first.