Add version number to output files with meta info

[kvid]

This is a follow-up to the version number part of #173 to also tag the .gv and .html output files with version number.
The last few HTML validation errors remaining from #97 was also removed in the process.

[formatc1702]

This is a good idea and I'm willing to include it in v0.2!

[kvid]

I'm sorry that the two last commits are slightly off topic, but the reasoning is:

• It didn't feel right to define the application name and URL once again when writing the meta tag (ref DRY), and with your Add version number to output files with meta info #177 (comment) in mind, I searched for the application name in the code and found it written a lot of places - written 3 different ways: WireViz, Wireviz, and wireviz. Therefore, I moved the definition to a common file and imported these constants where needed.
• When validating the HTML meta tag, I first added a title tag to remove one of the errors, and finally I found a minor change of the HTML BOM that removed all the remaining errors. Do you want me to move this last commit to a separate PR, or should I just expand the scope slightly in the PR description?

[formatc1702]

I'm sorry that the two last commits are slightly off topic, but the reasoning is:

• It didn't feel right to define the application name and URL once again when writing the meta tag (ref DRY), and with your #177 (comment) in mind, I searched for the application name in the code and found it written a lot of places - written 3 different ways: WireViz, Wireviz, and wireviz. Therefore, I moved the definition to a common file and imported these constants where needed.

I appreciate the attention to detail, and I agree having a standardized way to write the app's name (WireViz) is good.
However, defining this as a constant and then referencing it a couple of times, and especially piecing together the URL from it (URL = 'https://github.com/formatc1702/' + APP_NAME), is overdoing it and does not contribute to simplifying the code...
TBH I'd rather just correct the instances where the name/URL occurs, and make sure future PRs stick to the convention... perhaps adding a note to the contribution guidelines.
If the name/URL should ever change, a project-wide search&replace will be easy enough, I don't mind having it hardcoded in 2-3 places.
See my comments in the code. Maybe this feature will increase in value in the future :)

• When validating the HTML meta tag, I first added a title tag to remove one of the errors, and finally I found a minor change of the HTML BOM that removed all the remaining errors. Do you want me to move this last commit to a separate PR, or should I just expand the scope slightly in the PR description?

Hehe, I doubt this would have bothered anyone, and I doubt that the ALIGN attribute is ever going to truly stop working, but I am OK with fixing the validation error in this way. Up to you to create a new PR or not... I am more concerned with the commit history (which would end up looking pretty much the same either way). If you want to be extra clean about it, I guess a PR is the way to go.

[formatc1702]

Looks good, couldn't find any remaining references that would need fixing.

Much appreciated!