Nelson Menezes

Title says it all, really 😄. This should address #24 (and includes some of the changes suggested by @tlvince in there) as well as #136

Some pseudo-classes (`:first-child`, `:nth-child`…) make perfect sense as target selectors. Others, not so much: `:valid`, `:hover`, `:lang()`. Likewise, most pseudo-elements don't work well as targets (`::before`, `::after`), but we could...