split code into separate module and tool

[satta]

This PR restructures the code of icdiff to provide a separate icdiff module which is installed separately in a Python module directory as well as as script icdiff which is meant to go into the $PATH. This is IMHO another (cleaner?) way to address #72, #73 etc. without having to add the .py extension to the main script.
My changed variant still runs the tests successfully in the local cloned as well as the installed version.
Comments? Maybe there is a more Pythonic way to do this ;)

[jeffkaufman]

Currently http://www.jefftk.com/icdiff has "install for mac/linux" with:

curl -s https://raw.githubusercontent.com/jeffkaufman/icdiff/release-1.8.1/icdiff \
  | sudo tee /usr/local/bin/icdiff > /dev/null \
  && sudo chmod ugo+rx /usr/local/bin/icdiff

I'd really like to keep an installation option like this available, where people can run a simple command and end up with an icdiff executable installed.

I'm not really sure what the right way to do this is?

[satta]

My approach would be to upload the new split icdiff package to PyPI and thd then change the icdiff web page to suggest using pip:

sudo pip install icdiff

This would install both the module and the executable (into /usr/local/bin by default). It does require pip to be present for installation, but IMHO that's quite common for Python stuff anyway nowadays; the current approach also needs curl as a second dependency.

[vnitinv]

sudo pip install icdiff

This is already working. With having both option. icdiff working as commandline tool and as module.
We needed to change diff function to work in module way. check this #75

[xrat]

I'd also very much prefer that icdiff could be used in both ways. I agree that pip is "quite common nowadays", though, on my production machines I still refuse to run pip as root. Here I prefer single file scripts that I can easily review, install and update by means of http and cat. In fact, I wouldn't be following Jeff's icdiff if it wasn't for the fact that he offered a single file solution.

[satta]

Ah, I see (concerning #75)... so if I understand the setup.py correctly, icdiff.py is installed in the module path and an icdiff wrapper script without .py extension is created in the $PATH that just calls the start function? That is indeed cool and a much better solution 👍 Thanks!

[vnitinv]

You got it right @satta

[lurch]

FYI the "proper" way to do this is using setuptools, see http://python-packaging.readthedocs.io/en/latest/command-line-scripts.html and also codespell-project/codespell#136 as this allows it to work from the command-line on all platforms (e.g. by automatically creating icdiff.bat on Windows).