patch 9.1.0836: The vimtutor can be improved

Problem:  the vimtutor can be improved
Solution: port and include the interactive vimtutor plugin from Neovim
          (by Felipe Morales) (Yegappan Lakshmanan)

closes: #6414

Signed-off-by: Christian Brabandt <cb@256bit.org>
Signed-off-by: Yegappan Lakshmanan <yegappan@yahoo.com>

runtime/ftplugin/tutor.vim

@@ -0,0 +1,45 @@
+" vim: fdm=marker
+
+" Base: {{{1
+call tutor#SetupVim()
+
+" Buffer Settings: {{{1
+setlocal noreadonly
+if !exists('g:tutor_debug') || g:tutor_debug == 0
+    setlocal buftype=nofile
+    setlocal concealcursor+=inv
+    setlocal conceallevel=2
+else
+    setlocal buftype=
+    setlocal concealcursor&
+    setlocal conceallevel=0
+endif
+setlocal noundofile
+
+setlocal keywordprg=:help
+setlocal iskeyword=@,-,_
+
+" The user will have to enable the folds himself, but we provide the foldexpr
+" function.
+setlocal foldmethod=manual
+setlocal foldexpr=tutor#TutorFolds()
+setlocal foldlevel=4
+
+" Load metadata if it exists: {{{1
+if filereadable(expand('%').'.json')
+    call tutor#LoadMetadata()
+endif
+
+" Mappings: {{{1
+
+call tutor#SetNormalMappings()
+
+" Checks: {{{1
+
+sign define tutorok text=✓ texthl=tutorOK
+sign define tutorbad text=✗ texthl=tutorX
+
+if !exists('g:tutor_debug') || g:tutor_debug == 0
+    call tutor#ApplyMarks()
+    autocmd! TextChanged,TextChangedI <buffer> call tutor#ApplyMarksOnChanged()
+endif