XML Grammar for tree-sitter

Based on the W3C XML 1.0 recommendation

Example files come from W3C samples, generated data, and wikimedia dumps.

Finished sections from the XML specification:

• Document
• Character Range (currently doing with /./)
• White Space (currently doing with /\s/)
• Names and Tokens
• Literals
• Character Data
• Comments
• Processing Instructions (haven't quite finished the pi_target definition)
• CDATA Sections (not sure about the cdata element, I need to test it more)
• Prolog
• Document Type Definition
• External Subset
• Standalone Document Declaration
• Language Identification
• Element
• Start-tag
• End-tag
• Content of Elements
• Tags for Empty Elements
• Element Type Declaration
• Element-content Models
• Mixed-content Declaration
• Attribute-list Declaration
• Attribute Types
• Enumerated Attribute Types
• Attribute Defaults
• Conditional Section ($.ignore might not be good enough)
• Character Reference
• Entity Reference
• Entity Declaration
• External Entity Declaraion
• Text Declaration
• Well-Formed External Parsed Entity
• Encoding Declaration
• Encoding Declaration
• Notation Declarations
• Characters

Note that these just mean I have literally written them in, I'm still working on organization and figuring out what needs to be visible/hidden. Help is appreciated!