refactor: Replace .vim files with .lua

Closes #525

ftplugin/org.lua

@@ -0,0 +1,35 @@
+if vim.b.did_ftplugin then
+  return
+end
+---@diagnostic disable-next-line: inject-field
+vim.b.did_ftplugin = true
+
+local config = require('orgmode.config')
+
+config:setup_mappings('org')
+config:setup_mappings('text_objects')
+config:setup_foldlevel()
+
+vim.bo.modeline = false
+vim.opt_local.fillchars:append('fold: ')
+vim.opt_local.foldmethod = 'expr'
+vim.opt_local.foldexpr = 'nvim_treesitter#foldexpr()'
+vim.opt_local.foldtext = 'v:lua.require("orgmode.org.indent").foldtext()'
+vim.opt_local.formatexpr = 'v:lua.require("orgmode.org.format")()'
+vim.opt_local.omnifunc = 'v:lua.orgmode.omnifunc'
+vim.opt_local.commentstring = '# %s'
+
+_G.orgmode.omnifunc = function(findstart, base)
+  return require('orgmode.org.autocompletion.omni').omnifunc(findstart, base)
+end
+
+local abbreviations = {
+  [':today:'] = "require('orgmode.objects.date').today():to_wrapped_string(true)",
+  [':now:'] = "require('orgmode.objects.date').now():to_wrapped_string(true)",
+  [':itoday:'] = "require('orgmode.objects.date').today():to_wrapped_string(false)",
+  [':inow:'] = "require('orgmode.objects.date').now():to_wrapped_string(false)",
+}
+
+for abbrev, cmd in pairs(abbreviations) do
+  vim.cmd.inoreabbrev(('<silent><buffer> %s <C-R>=luaeval("%s")<CR>'):format(abbrev, cmd))
+end

indent/org.lua

@@ -0,0 +1,10 @@
+if vim.b.did_indent then
+  return
+end
+---@diagnostic disable-next-line: inject-field
+vim.b.did_indent = true
+
+vim.bo.indentexpr = 'v:lua.require("orgmode.org.indent").indentexpr()'
+vim.bo.lisp = false
+vim.bo.smartindent = false
+vim.bo.autoindent = true