feat!: Rewrite user configuration.

[kylechui]

BREAKING CHANGE

This commit will deprecate the existing setup and buffer_setup function calls, in line with this blog post. I believe that plugins, by default, should merely expose functionality but not actively modify user configuration at all. The goal is to have the installation script in the README contain the current "default" configuration, and any changes can be made by users directly. While this results in more code for the end user, I think that the reduced complexity and layers of abstraction will ultimately help users better understand the plugin and have more control for how it behaves.

The changes will be:

• setup(...) → vim.g.nvim_surround
• buffer_setup(...) → vim.b.nvim_surround