Split default IO down into to/from href methods

This allows subclasses of DefaultStacIO to not have to re-impelment link
resolution if they don't want to.

Author: gadomski

pystac/stac_io.py

@@ -176,7 +176,9 @@ def read_text(
             href = source.get_absolute_href()
             if href is None:
                 raise IOError(f"Could not get an absolute HREF from link {source}")
+        return self.read_text_from_href(href, *args, **kwargs)
 
+    def read_text_from_href(self, href: str, *args: Any, **kwargs: Any) -> str:
         parsed = urlparse(href)
         if parsed.scheme != "":
             try:
@@ -197,7 +199,11 @@ def write_text(
             href = dest.get_absolute_href()
             if href is None:
                 raise IOError(f"Could not get an absolute HREF from link {dest}")
+        return self.write_text_to_href(href, txt, *args, **kwargs)
 
+    def write_text_to_href(
+        self, href: str, txt: str, *args: Any, **kwargs: Any
+    ) -> None:
         dirname = os.path.dirname(href)
         if dirname != "" and not os.path.isdir(dirname):
             os.makedirs(dirname)