add neoscroll plugin with circ easing

lua/plugins/neoscroll.lua

@@ -0,0 +1,47 @@
+return {
+  'karb94/neoscroll.nvim',
+  config = function()
+    local neoscroll = require 'neoscroll'
+    neoscroll.setup {
+      mappings = {
+        '<C-u>',
+        '<C-d>',
+        '<C-b>',
+        '<C-f>',
+        'zt',
+        'zz',
+        'zb',
+      },
+      easing = 'circ',
+      respect_scrolloff = true,
+    }
+
+    local keymap = {
+      ['<C-u>'] = function()
+        neoscroll.ctrl_u { duration = 200 }
+      end,
+      ['<C-d>'] = function()
+        neoscroll.ctrl_d { duration = 200 }
+      end,
+      ['<C-b>'] = function()
+        neoscroll.ctrl_b { duration = 300 }
+      end,
+      ['<C-f>'] = function()
+        neoscroll.ctrl_f { duration = 300 }
+      end,
+      ['zt'] = function()
+        neoscroll.zt { half_win_duration = 100 }
+      end,
+      ['zz'] = function()
+        neoscroll.zz { half_win_duration = 100 }
+      end,
+      ['zb'] = function()
+        neoscroll.zb { half_win_duration = 100 }
+      end,
+    }
+    local modes = { 'n', 'v', 'x' }
+    for key, func in pairs(keymap) do
+      vim.keymap.set(modes, key, func)
+    end
+  end,
+}