feat: add enabled field for styles class

- updated README.md to reflect new option

Defaults to true. If enabled is false remove all styles. Allows for
easier modification for users who do not want any styles with the
colorscheme.

README.md

@@ -271,6 +271,13 @@ require('solarized').setup({
 })
 ```
 
+You can also disable all highlight group styles.
+```lua
+require('solarized').setup({
+    styles = { enabled = false } },
+})
+```
+
 ## Config Highlights
 
 The `highlights` config allows you to customize the highlights groups.

lua/solarized/config.lua

@@ -11,6 +11,7 @@
 ---@field enabled? boolean
 
 ---@class solarized.styles
+---@field enabled? boolean
 ---@field types? vim.api.keyset.highlight
 ---@field functions? vim.api.keyset.highlight
 ---@field parameters? vim.api.keyset.highlight

lua/solarized/init.lua

@@ -10,6 +10,19 @@ M.config = require 'solarized.config'
 
 M.setup = function(config)
   M.config = vim.tbl_deep_extend('force', M.config, config)
+
+  if M.config.styles.enabled == false then
+    M.config.styles = {
+      types = { italic = false, bold = false },
+      functions = { italic = false, bold = false },
+      parameters = { italic = false, bold = false },
+      comments = { italic = false, bold = false },
+      strings = { italic = false, bold = false },
+      keywords = { italic = false, bold = false },
+      variables = { italic = false, bold = false },
+      constants = { italic = false, bold = false },
+    }
+  end
 end
 
 M.load = function()