We were ignoring singleton tags like "input" tags in
html-grep. This was an artifact of our tokenizer originally
being built to check indentation of templates, for which
singleton tags had been a distraction. This fix actually cleans up
the template checking logic as well, since it can now rely
on the tokenizer to classify special tags and singleton tags.
The tokenizer is more complete and more specific.
`tools/lint-all` now calls the new `tools/check-css`
The css_parser library parsers CSS into a data structure
that remembers line numbers and columns of semantically
meaningful tokens and adjoining white space/tokens. It
is intended to be used for various linting tasks.
The file `tools/check-css` runs a few files through the
parser and makes sure they round trip. This has some value
right away, as files that fail to parse will cause an
exception to be thrown and thus alert developers to syntax
errors. We expect to grow this into more advanced linting
tasks eventually.