Add user command and function to toggle this plugin

## Details

Feature suggested through: #4

Sometimes user would like to see raw view in normal mode.

Created a `toggle` which essentially enables / disables this entire plugin.

Wrapped this in user command `RenderMarkdownToggle`.

Author: MeanderingProgrammer

Diff for: README.md

@@ -101,6 +101,12 @@ require('render-markdown').setup({
 })
 ```
 
+# Commands
+
+`:RenderMarkdownToggle` - Switch between enabling & disabling this plugin
+
+- Function can also be accessed directly through `require('render-markdown').toggle()`
+
 # Purpose
 
 There are many existing markdown rendering plugins in the Neovim ecosystem. However,

Diff for: lua/render-markdown/init.lua

@@ -75,9 +75,10 @@ function M.setup(opts)
         },
     }
     state.config = vim.tbl_deep_extend('force', default_config, opts or {})
+    state.enabled = true
 
     -- Call immediately to re-render on LazyReload
-    M.refresh()
+    vim.schedule(M.refresh)
 
     vim.api.nvim_create_autocmd({
         'FileChangedShellPost',
@@ -91,16 +92,36 @@ function M.setup(opts)
             vim.schedule(M.refresh)
         end,
     })
+
+    vim.api.nvim_create_user_command(
+        'RenderMarkdownToggle',
+        M.toggle,
+        { desc = 'Switch between enabling & disabling render markdown plugin' }
+    )
 end
 
 M.namespace = vim.api.nvim_create_namespace('render-markdown.nvim')
 
+M.toggle = function()
+    if state.enabled then
+        state.enabled = false
+        vim.schedule(M.clear)
+    else
+        state.enabled = true
+        -- Call to refresh must happen after state change
+        vim.schedule(M.refresh)
+    end
+end
+
 M.clear = function()
     -- Remove existing highlights / virtual text
     vim.api.nvim_buf_clear_namespace(0, M.namespace, 0, -1)
 end
 
 M.refresh = function()
+    if not state.enabled then
+        return
+    end
     if not vim.tbl_contains(state.config.file_types, vim.bo.filetype) then
         return
     end

Diff for: lua/render-markdown/state.lua

@@ -21,6 +21,7 @@
 ---@field public highlights Highlights
 
 ---@class State
+---@field enabled boolean
 ---@field config Config
 local state = {}
 return state