pyln: Change the setup.py file not to import the package

This would lead to errors about missing dependencies when attempting
to install using `pyhon setup.py install`. This is because the
`setup.py` file effectively is the manifest file used to discover
which dependencies are needed, so when using it to detect dependencies
we obviously don't have them yet.

See https://packaging.python.org/guides/single-sourcing-package-version/

contrib/pyln-proto/setup.py

@@ -1,16 +1,34 @@
 from setuptools import setup
-from pyln.proto import __version__
+import codecs
 import io
+import os.path
 
 
 with io.open('README.md', encoding='utf-8') as f:
     long_description = f.read()
 
+
 with io.open('requirements.txt', encoding='utf-8') as f:
     requirements = [r for r in f.read().split('\n') if len(r)]
 
+
+def read(rel_path):
+    here = os.path.abspath(os.path.dirname(__file__))
+    with codecs.open(os.path.join(here, rel_path), 'r') as fp:
+        return fp.read()
+
+
+def get_version(rel_path):
+    for line in read(rel_path).splitlines():
+        if line.startswith('__version__'):
+            delim = '"' if '"' in line else "'"
+            return line.split(delim)[1]
+    else:
+        raise RuntimeError("Unable to find version string.")
+
+
 setup(name='pyln-proto',
-      version=__version__,
+      version=get_version("pyln/proto/__init__.py"),
       description='Pure python implementation of the Lightning Network protocol',
       long_description=long_description,
       long_description_content_type='text/markdown',