diff --git a/typed_environment_configuration/typed_environment_configuration.py b/typed_environment_configuration/typed_environment_configuration.py
index 6429966..04e33ac 100644
--- a/typed_environment_configuration/typed_environment_configuration.py
+++ b/typed_environment_configuration/typed_environment_configuration.py
@@ -73,6 +73,10 @@ class StringVariable(Variable):
     _value_type = typepy.type.String
     _strict_level = 0
 
+class IntegerVariable(Variable):
+    _value_type = typepy.type.Integer
+    _strict_level = 1
+
 
 class StringListVariable(Variable):
     """

diff --git a/tests/test_typed_environment_configuration.py b/tests/test_typed_environment_configuration.py
index ad2babf..cb88eed 100644
--- a/tests/test_typed_environment_configuration.py
+++ b/tests/test_typed_environment_configuration.py
@@ -9,7 +9,11 @@ import os
 
 from typed_environment_configuration import *
 
-_ENVVARS = [BoolVariable("DEBUG"), StringVariable("DEFAULT_STRING", default="")]
+_ENVVARS = [
+    BoolVariable("DEBUG"),
+    IntegerVariable("INT_VAR"),
+    StringVariable("DEFAULT_STRING", default=""),
+]
 
 _PREFIXED_ENVVARS = [
     StringVariable("PREFIXED_VERSION"),
@@ -18,12 +22,14 @@ _PREFIXED_ENVVARS = [
 
 v = vars()
 
+
 class TestTyped_environment_configuration(unittest.TestCase):
     """Tests for `typed_environment_configuration` package."""
 
     def setUp(self):
         """Set up test fixtures, if any."""
         os.environ["DEBUG"] = "True"
+        os.environ["INT_VAR"] = "10"
         os.environ["PREFIXED_VERSION"] = "1.2.3"
 
         FillVars(_ENVVARS, v)
@@ -36,6 +42,10 @@ class TestTyped_environment_configuration(unittest.TestCase):
         """Tests that setting boolean variable in env creates a python variable DEBUG=True"""
         self.assertEqual(DEBUG, True)
 
+    def test_IntegerVariable(self):
+        """Tests that setting integer variable in env creates a python variable NUM_VAR=10"""
+        self.assertEqual(INT_VAR, 10)
+
     def test_PrefixedVariable(self):
         """Tests a prefixed variable"""
         self.assertEqual(VERSION, "1.2.3")

Add integer number variable class
* Typed Environment Configuration version: 0.1.3
* Python version: 3.8.3
* Operating System: alpine linux

### Description

There is no way to set integer variable from environment variables currently.

### What I Did


```
from os import getenv
CACHE_MIDDLEWARE_SECONDS = int(getenv("DJANGO_CACHE_MIDDLEWARE_SECONDS", default=0))
```

tests/test_typed_environment_configuration.py::TestTyped_environment_configuration::test_BoolVariable tests/test_typed_environment_configuration.py::TestTyped_environment_configuration::test_DefaultVariable tests/test_typed_environment_configuration.py::TestTyped_environment_configuration::test_IntegerVariable tests/test_typed_environment_configuration.py::TestTyped_environment_configuration::test_PrefixedVariable