Make package PEP 561 compliant; add typehint stub file

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## Development
 
+* Made this package PEP 561 compliant (#49).
 * Release GIL during the computation of the CRC32C hash. A new `gil_release_mode` argument lets users choose between always/never/automatically releasing it (#47).
 * Add keyword support to `crc32c` function (`crc32c(data, value=0, gil_release_mode=-1)`).
 * Turned ``crc32c`` from a module-only distribution into a package,

MANIFEST.in

@@ -1,3 +1,5 @@
 include LICENSE*
 include AUTHORS*
 include src/crc32c/ext/*.h
+include src/crc32c/*.pyi
+include src/crc32c/py.typed

setup.py

@@ -67,5 +67,6 @@
       classifiers=classifiers,
       packages=['crc32c'],
       package_dir={'': 'src'},
+      include_package_data=True,
       ext_modules=[crcmod_ext],
       test_suite="test")

src/crc32c/__init__.pyi

@@ -0,0 +1,7 @@
+from collections.abc import Buffer
+
+big_endian: int
+hardware_based: bool
+
+def crc32(data: Buffer, value: int = 0, gil_release_mode: int = -1) -> int: ...
+def crc32c(data: Buffer, value: int = 0, gil_release_mode: int = -1) -> int: ...