Strip-tags

- Fixed an error when run against files using an encoding other than UTF-8. Thanks, [kmad](https://github.com/kmad). [#7](https://github.com/simonw/strip-tags/issues/7)

- New bundles for keeping tags: `-t tables` keeps table tags, `-t lists` keeps list tags. [18](https://github.com/simonw/strip-tags/issues/18)
- `strip-tags -r/--remove` option for entirely removing the content of specified selectors. [24](https://github.com/simonw/strip-tags/issues/24)
- Fixed a bug where `<!-- comment -->` text was incorrectly included in the stripped output. [25](https://github.com/simonw/strip-tags/issues/25)

- Fixed bug where `strip-tags -t pre` failed to keep the `<pre>` tag markup.
- Better Python library example code.

- This package can now be used as a Python library: `from strip_tags import strip_tags`. Thanks, Benjamin Kirkbride. [9](https://github.com/simonw/strip-tags/issues/9)
- Text inside `<pre>` elements will no longer have its whitespace modified by `--minify`. [12](https://github.com/simonw/strip-tags/issues/12)
- `strip-tags article --first` will now return content from just the first element matching the `article` selector. [13](https://github.com/simonw/strip-tags/issues/13)
- `-t/--keep-tag` can be used to specify tags that should have their markup preserved in the output. `-t hs` and `-t structure` and `-t metadata` can be used as shortcuts to specify a bundle of tags at once. [14](https://github.com/simonw/strip-tags/issues/14)

- Tags with invisible content such as `<script>` and `<style>` are now omitted from the output. [4](https://github.com/simonw/strip-tags/issues/4)
- Images are now replaced by the content of their `alt=` attribute, if available. [5](https://github.com/simonw/strip-tags/issues/5)
- New `-m/--minify` option for minifying white space in the output. [6](https://github.com/simonw/strip-tags/issues/6)

- Design change: tool now accepts CSS selectors as optional arguments, input file can be specified using the new `-i/--input` option. [3](https://github.com/simonw/strip-tags/issues/3)