Fixes to gmi2html

Now that I'm using this as a lib I've discovered some weird and counterintuitive design choices that didn't work well in that context.

• gmi2html.convert now takes an array of strings as input instead of filename(s).
• I had apparently forgot a .gitignore file, resulting in a whole lot of unnecessary files being included in the repo. This is fixed now.
• I bumped the version number to 1.1 to reflect that fixes have been made.

The tool still works the same on the command line, of course.

-- CC0 ew0k, 2022-01-19