Add basic type stubs (#221) (#215)

* feat: add basic type stubs

* feat: add types for constants

* feat: add type for `MarkdownConverter` class

* ci: add basic job for checking types

* feat: add new constant

* ci: install types as required

* ci: install types package manually

* test: add strict coverage for types

* fix: allow `strip_document` to be `None`

* feat: expand types for MarkdownConverter

* fix: do not use `Unpack` as it requires Python 3.12

* feat: define `MarkdownConverter#convert_soup`

* feat: improve type for `code_language_callback`

* chore: add end-of-file newline

* refactor: use `Union` for now

markdownify/__init__.pyi

@@ -0,0 +1,77 @@
+from _typeshed import Incomplete
+from typing import Callable, Union
+
+ATX: str
+ATX_CLOSED: str
+UNDERLINED: str
+SETEXT = UNDERLINED
+SPACES: str
+BACKSLASH: str
+ASTERISK: str
+UNDERSCORE: str
+LSTRIP: str
+RSTRIP: str
+STRIP: str
+STRIP_ONE: str
+
+
+def markdownify(
+    html: str,
+    autolinks: bool = ...,
+    bs4_options: str = ...,
+    bullets: str = ...,
+    code_language: str = ...,
+    code_language_callback: Union[Callable[[Incomplete], Union[str, None]], None] = ...,
+    convert: Union[list[str], None] = ...,
+    default_title: bool = ...,
+    escape_asterisks: bool = ...,
+    escape_underscores: bool = ...,
+    escape_misc: bool = ...,
+    heading_style: str = ...,
+    keep_inline_images_in: list[str] = ...,
+    newline_style: str = ...,
+    strip: Union[list[str], None] = ...,
+    strip_document: Union[str, None] = ...,
+    strip_pre: str = ...,
+    strong_em_symbol: str = ...,
+    sub_symbol: str = ...,
+    sup_symbol: str = ...,
+    table_infer_header: bool = ...,
+    wrap: bool = ...,
+    wrap_width: int = ...,
+) -> str: ...
+
+
+class MarkdownConverter:
+    def __init__(
+        self,
+        autolinks: bool = ...,
+        bs4_options: str = ...,
+        bullets: str = ...,
+        code_language: str = ...,
+        code_language_callback: Union[Callable[[Incomplete], Union[str, None]], None] = ...,
+        convert: Union[list[str], None] = ...,
+        default_title: bool = ...,
+        escape_asterisks: bool = ...,
+        escape_underscores: bool = ...,
+        escape_misc: bool = ...,
+        heading_style: str = ...,
+        keep_inline_images_in: list[str] = ...,
+        newline_style: str = ...,
+        strip: Union[list[str], None] = ...,
+        strip_document: Union[str, None] = ...,
+        strip_pre: str = ...,
+        strong_em_symbol: str = ...,
+        sub_symbol: str = ...,
+        sup_symbol: str = ...,
+        table_infer_header: bool = ...,
+        wrap: bool = ...,
+        wrap_width: int = ...,
+    ) -> None:
+        ...
+  
+    def convert(self, html: str) -> str:
+        ...
+
+    def convert_soup(self, soup: Incomplete) -> str:
+        ...