Tree-sitter parser for YANG 1.1

Tree-sitter parser implementation for YANG, a data modeling language used to model configuration data, state data, Remote Procedure Calls and notifications for network management protocols.

https://datatracker.ietf.org/doc/html/rfc7950

TODO

• Implement strings properly (Done: #3)

  Currently the string parsing is just copied from the Javascript grammar and slightly modified to hide escape sequences in single quoted strings.

  Strings are well documented in the YANG RFC and should be properly implemented in the grammar:

  https://datatracker.ietf.org/doc/html/rfc7950#section-6.1.3

• Support quoted keypaths

  Parsing keypaths currently works well, but quoted keypaths are currently parsed as strings.

  It should be possible to parse quoted keypaths by creating a custom statement symbol for the keywords that expect keypaths (like augment, leafref and so on.)