Add svelte/sort-attributes rule

[ota-meshi]

This PR adds svelte/sort-attributes rule that enforce order of attributes.

close #150

[tivac]

Looked at the docs, love where this is headed and very impressed how fast it came together!

Quick question about the config format, I assume this uses standard regex flags so the /u usage in the examples isn't always necessary unless you need to match extended Unicode characters in attributes?

[ota-meshi]

Thank you for checking! I will proceed with the implementation as it is 😉.

The u flag is not required. I like to use the u flag as similar to strict mode. The u flag will find the wrong use of the regex and let me know as an error. For example, new RegExp ('\\w{1,5', 'u')