Use Vim's pythonx mechanism

Move jedi_vim.py and the jedi submodule into pythonx, which gets added
to Vim's internal sys.path.  While jedi cannot be imported directly from
there, it still makes sense for consistency.

autoload/jedi.vim

@@ -152,29 +152,20 @@ function! jedi#setup_py_version(py_version) abort
 
     execute 'command! -nargs=1 PythonJedi '.cmd_exec.' <args>'
 
-    let s:init_outcome = 0
-    PythonJedi << EOF
-try:
-    import vim
-    import os, sys
-    jedi_path = os.path.join(vim.eval('expand(s:script_path)'), 'jedi')
-    sys.path.insert(0, jedi_path)
-
-    jedi_vim_path = vim.eval('expand(s:script_path)')
-    if jedi_vim_path not in sys.path:  # Might happen when reloading.
-        sys.path.insert(0, jedi_vim_path)
-except Exception as excinfo:
-    vim.command('let s:init_outcome = "error when adding to sys.path: {0}: {1}"'.format(excinfo.__class__.__name__, excinfo))
-else:
-    try:
-        import jedi_vim
-    except Exception as excinfo:
-        vim.command('let s:init_outcome = "error when importing jedi_vim: {0}: {1}"'.format(excinfo.__class__.__name__, excinfo))
-    else:
-        vim.command('let s:init_outcome = 1')
-    finally:
-        sys.path.remove(jedi_path)
-EOF
+    let init_lines = [
+          \ 'import vim',
+          \ 'vim.command(''let s:init_outcome = 0'')',
+          \ 'try:',
+          \ '    import jedi_vim',
+          \ 'except Exception as exc:',
+          \ '    vim.command(''let s:init_outcome = "could not import jedi_vim: {0}: {1}"''.format(exc.__class__.__name__, exc))',
+          \ 'else:',
+          \ '    vim.command(''let s:init_outcome = 1'')']
+    try
+        exe 'PythonJedi exec('''.escape(join(init_lines, '\n'), "'").''')'
+    catch
+        throw printf('jedi#setup_py_version: failed to run Python for initialization: %s.', v:exception)
+    endtry
     if !exists('s:init_outcome')
         throw 'jedi#setup_py_version: failed to run Python for initialization.'
     elseif s:init_outcome isnot 1