Move irc library requirement to setup.py

I'm so out of practice at building libraries that I neglected to mark
irc as a dependency in the setup.py file.

Closes #1

Author: bd808

requirements.txt

@@ -1 +1 @@
-irc>=15.0.3
+-e .

setup.py

@@ -30,6 +30,9 @@
     packages=setuptools.find_packages(
         exclude=['docs', 'tests', 'tests.*']),
     include_package_data=True,
+    install_requires=[
+        'irc>=15.0.3',
+    ],
     extras_require={
         'testing': tests_require,
     },