replace underscores for dashed tags

pyproject.toml

@@ -1,6 +1,6 @@
 [tool.poetry]
 name = "tagz"
-version = "0.2.2"
+version = "0.2.3"
 description = "tagz is a html tags builder"
 authors = ["Dmitry Orlov <me@mosquito.su>"]
 license = "MIT"

tagz.py

@@ -169,6 +169,7 @@ def __init__(self, defaults: Mapping[str, Mapping[str, Any]]):
         self.__defaults: Mapping[str, Mapping[str, Any]] = MappingProxyType(defaults)
 
     def __getitem__(self, tag_name: str) -> Type[TagInstance]:
+        tag_name = tag_name.lower().replace("_", "-")
         return create_tag_class(tag_name, **self.__defaults.get(tag_name, {}))
 
     def __getattr__(self, tag_name: str) -> Type[TagInstance]:

tests/test_html.py

@@ -36,6 +36,9 @@ def test_tag_string_representation():
     assert tag.to_string(pretty=True) == (
         '<p>\n\tHello, World!\n\t<a href="/">\n\t\tgo to index\n\t</a>\n\t<i/>\n</p>\n'
     )
+    assert html.my_custom_tag is html.my_custom_tag
+    assert str(html.my_custom_tag()) == "<my-custom-tag/>"
+    assert str(html.my_custom_tag("test")) == "<my-custom-tag>test</my-custom-tag>"
 
 
 def test_html_generation(sample_html_page):