Add uninstaller

Closes #2

Also document installer, fix some formatting issues, add encoding to an
open(), and remove an obsolete TODO.

unpack.py

@@ -49,6 +49,7 @@ def _mkdir_p(parts: Sequence[str]) -> None:
 
     # (end code derived from `pathlib`)
 
+
 class InvalidFileError(BaseException):
     """
     CircuitPack package file is invalid.
@@ -77,8 +78,9 @@ class _ResponseFile:  # pylint: disable=too-few-public-methods
         return response
 
 
-def unpack(package: Union[BinaryIO, _ResponseFile], target: str) -> Iterable[str]:
+def unpack(
-    # TODO: add a way to limit where packages can store files?
+    package: Union[BinaryIO, _ResponseFile], target: str
+) -> Iterable[str]:
     """
     Unpack the given file-like object `package` into the directory `target`,
     which may, but is not required to, already exist. Return the unpacked
@@ -135,14 +137,42 @@ def unpack_url(url: str, target: str) -> Iterable[str]:
 
     return unpack(_ResponseFile(requests.get(url)), target)
 
-def install(name: str, version_hash: str, repo: str, target: str, records: str) -> None:
+
+def install(
+    name: str, version_hash: str, repo: str, target: str, records: str
+) -> None:
+    """
+    Download version `version_hash` of package `name` from `repo`, unpack it
+    into the directory `target`, and create a record file in `records`.
+    """
+
     if not repo.endswith("/"):
         repo = repo + "/"
 
     file_names = unpack_url(f"{repo}{name}.{version_hash}.cpa", target)
 
-    with open(f"{records}/{name}", "w+") as f:
+    with open(f"{records}/{name}", "w+", encoding="utf-8") as record:
-        f.write(f"{version_hash}\n")
+        record.write(f"{version_hash}\n")
 
         for file_name in file_names:
-            f.write(f"{file_name}\n")
+            record.write(f"{file_name}\n")
+
+
+def uninstall(name: str, target: str, records: str) -> None:
+    """
+    Uninstall package `name` from `target` using the information stored in
+    `records`.
+    """
+
+    with open(f"{records}/{name}", "r", encoding="utf-8") as record:
+        record.readline() # Skip over version hash
+
+        while True:
+            file_name = record.readline().strip()
+
+            if file_name:
+                os.remove(f"{target}/{file_name}")
+            else:
+                break
+
+    os.remove(f"{records}/{name}")