Use attribute based scoping instead of classes; small optimizaitons

[infogulch]

• Only support using me. The 'extra flexibility' is unnecessary and distracting. If users want a different selector then they can edit it, it's only 12 lines of code.
• Use data attributes to identify the parent scope id and select it; this is less likely to interact with existing css tooling and classes, and makes it easier to identify by eye.
• Combine parent and child scope id assignment and currentScopeId increment, reducing the size of the script by 2 lines.
• Only creates a parent's scope id once, multiple scoped style children will share the same id.
• Adjust the regexes to be more selective about what to replace