[ANN] Shape Expressions 2.1 release

The ShEx community group is happy to announce the release of ShEx 2.1.

The new ShEx release consists of three deliverables:
 * Shape Expressions Language 2.1 http://shex.io/shex-semantics-20191008/
 * Shape Expressions Primer 2.1 http://shex.io/shex-primer-20191009/
 * Shape Expressions Test Suite 2.1 https://github.com/shexSpec/shexTest/
including 1089 validation tests, 99 negative syntax tests, 14 negative
structure tests and 432 schema conversion tests between ShExC, ShExJ and
ShExR(*).

The test suite has an Implementation Report including 4 of the 5
implementations: http://shexspec.github.io/shexTest/reports/2.1/

ShEx 2.1 is backwards compatible with ShEx 2.0. The major changes include:
 * `START` clauses in imported schemas are now ignored instead of throwing
an error
 * Added IMPORT functionality (round-trips between ShExC, ShExJ and ShExR).
http://shex.io/shex-primer-20191009/#import
 * Added language support in value sets.
http://shex.io/shex-primer-20191009/#value-sets
 * Updated definition of semantics to clarify recursion.
http://shex.io/shex-semantics-20191008/#validation
 * Added annotations and semantic actions to node constraints.
http://shex.io/shex-semantics-20191008/#prod-bracketedTripleExpr
 * ShExC grammar allows ()s around simple TripleConstraints.
 * Added hundreds of tests of schema, validation and structure tests.
 * Multi-line comments (/* … */).
http://shex.io/shex-semantics-20191008/#term-PASSED_TOKENS

ShEx is running as a W3C community group and is open for everyone
interested in the language and the related technologies to join at
https://www.w3.org/community/shex/

Best regards,
Dimitris Kontokostas, Andra Waagmeester on behalf of the ShEx W3C CG

(*) Sample of test additions since v2.0:
 * schema tests -
https://github.com/shexSpec/shexTest/blob/master/schemas/manifest.ttl#L3680-L3934
 * Validation tests -
https://github.com/shexSpec/shexTest/blob/master/validation/manifest.ttl#L15895-L16179
 *
https://github.com/shexSpec/shexTest/blob/master/validation/manifest.ttl#L11037-L11490