Switch from flask.Markup to MarkupSafe

[Flask 2.3.0](https://flask.palletsprojects.com/en/3.0.x/changes/#version-2-3-0)
deprecated its Markup class in favor of of MarkupSafe.  This causes an
import error when using Flask-FomanticUI with newer Flask releases.

Fixes juniors90#3

flask_fomanticui/core.py

@@ -29,7 +29,9 @@
 
 import warnings
 
-from flask import Blueprint, Markup, current_app, url_for
+from flask import Blueprint, current_app, url_for
+
+from markupsafe import Markup
 
 try:  # pragma: no cover
     from wtforms.fields import HiddenField

setup.py

@@ -29,7 +29,7 @@
 PATH = pathlib.Path(os.path.abspath(os.path.dirname(__file__)))
 
 
-REQUIREMENTS = ["Flask>=2.0.2"]
+REQUIREMENTS = ["Flask>=2.3.0", "markupsafe"]
 
 with open(PATH / "flask_fomanticui" / "__init__.py") as fp:
     for line in fp.readlines():