v2.0.0

[stevecheckoway]

With #112, I think I've finished everything that I wanted to get finished for 2.0.0.

The changelog is here but some highlights:

• Integrate gumbo to fix some long-standing issues
• Implement the latest version of the HTML standard
• Add hundreds of tests (with tens of thousands of assertions) to both gumbo itself and to Nokogumbo.
• Implement all of the error conditions specified in the standard and use the standard-specified code names for those that have them (about half do not have a name yet)
• Implement proper HTML fragment parsing
• Implement proper HTML serialization
• Fix Windows builds and add CI tests for them
• Fix Gentoo builds and add CI tests for them

Unless there's anything else that needs to be added, I think we should

• Change the version number in lib/nokogumbo/version.rb
• Add a corresponding section in CHANGELOG.md for 2.0.0
• Tag v2.0.0
• Push a new gem

[stevecheckoway]

https://rubygems.org/gems/nokogumbo/versions/2.0.0