[fix] Minor changes of command line options

[kvid]

1. The current help output:

usage: wireviz.py [-h] [-o OUTPUT] [--generate-bom] [--prepend-file YAML_FILE]
                  YAML_FILE

It seems, however, that the current implementation ignores --generate-bom, and I suggest we comment out that parser.add_argument() code line until it gets implemented to avoid any confusion.

Originally posted by @kvid in #111 (comment)

2. I also suggest adding an optional -b BRANCH argument to build_examples.py to enable comparing to and restoring from any branch or commit. That will help when e.g. reversing an unfortunate commit of generated files.

3. I have noticed that I quite often by a mistake write build_examples.py diff instead of build_examples.py compare - probably because I'm used to the git diff command. I therefore consider renaming the compare command to diff or create an alias so both commands will work. What are your opinions?

[kvid]

I also suggest including a -V command line option (and --version as an alias) to both wireviz.py and build_examples.py that output version information. In #157 -v was suggested, but that is often used for verbose mode, and both python and dot use -V for version information.

I suggest specifying the version number in __init__.py as done e.g. in the howdoi project. It is then important to not include code that import anything in the same file to avoid any issues when the file is also imported in setup.py.

I know you have argued against feature creep in #101 (comment), but I still feel this feature is important to include in v0.2 to later make it easy to identify the version in use when more than one version has been released. I'm sorry I didn't suggest this much earlier.

[formatc1702]

I 100% agree it's a good time to add version output now, so I am willing to include this in v0.2! Ideally we could get the version number from setup.py to avoid any discrepancies.

I don't mind changing compare to diff either.

Commenting out unused lines is perfectly reasonable.

Regarding the -b BRANCH option... feel free to implement it if you wish, you are probably the one who is using this feature most, and I don't mind having that option. I am not sure how hard it would be to implement/test this, so perhaps it is wise to do this as a separate PR that can be added at a later date in v >= 0.3. Up to you.