Use our own redbot.core.VersionInfo over distutils.StrictVersion (#2188)

* Implements our required subset of PEP 440 in redbot.core.VersionInfo
* Added unit tests for version string parsing and comparisons

Signed-off-by: Toby Harradine <tobyharradine@gmail.com>

tests/core/test_version.py

@@ -1,6 +1,36 @@
 from redbot import core
+from redbot.core import VersionInfo
 
 
 def test_version_working():
     assert hasattr(core, "__version__")
     assert core.__version__[0] == "3"
+
+
+# When adding more of these, ensure they are added in ascending order of precedence
+version_tests = (
+    "3.0.0a32.post10.dev12",
+    "3.0.0rc1.dev1",
+    "3.0.0rc1",
+    "3.0.0",
+    "3.0.1",
+    "3.0.1.post1.dev1",
+    "3.0.1.post1",
+    "2018.10.6b21",
+)
+
+
+def test_version_info_str_parsing():
+    for version_str in version_tests:
+        assert version_str == str(VersionInfo.from_str(version_str))
+
+
+def test_version_info_lt():
+    for next_idx, cur in enumerate(version_tests[:-1], start=1):
+        cur_test = VersionInfo.from_str(cur)
+        next_test = VersionInfo.from_str(version_tests[next_idx])
+        assert cur_test < next_test
+
+
+def test_version_info_gt():
+    assert VersionInfo.from_str(version_tests[1]) > VersionInfo.from_str(version_tests[0])