SETUP move code to src

This way we can ensure that the packaged code is tested.
See https://hynek.me/articles/testing-packaging/ or c62a78c015

+ DOC adapt doc to new structure and test doc with travis

setup.py

@@ -2,10 +2,18 @@
 
 import os
 import sys
-from setuptools import setup
+from setuptools import find_packages, setup
 from setuptools.command.test import test as test_command
 
 
+base_dir = os.path.dirname(__file__)
+src_dir = os.path.join(base_dir, "src")
+
+# When executing the setup.py, we need to be able to import ourselves, this
+# means that we need to add the src/ directory to the sys.path.
+sys.path.insert(0, src_dir)
+
+
 def read(fname):
     """read file from same path as setup.py"""
     return open(os.path.join(os.path.dirname(__file__), fname)).read()
@@ -58,9 +66,8 @@ setup(
         'receipt,',
     ],
     platforms='any',
-    packages=[
-        'escpos',
-    ],
+    package_dir={"": "src"},
+    packages=find_packages(where="src", exclude=["tests", "tests.*"]),
     package_data={'': ['COPYING']},
     classifiers=[
         'Development Status :: 4 - Beta',