Add readme, modify setup_grammar.py to show proper usage.

README.md

@@ -0,0 +1,71 @@
+# cratedb-sqlparse
+
+`Antlr4` is a parser generator for reading, processing and executing text, there are several
+target languages (Java, Python, JavaScript, Dart...) available. CrateDB uses the Java target.
+
+The repository holds libraries/packages created from some of those available languages, so
+far: `Python` and `JavaScript`.
+More might be added if needed in the future.
+
+These libraries allow you to parse Crate's SQL dialect without sending it to a CrateDB instance.
+
+- `Python`: https://github.com/crate/cratedb-sqlparse/tree/master/cratedb_sqlparse_py
+- `Javascript`: https://github.com/crate/cratedb-sqlparse/tree/master/cratedb_sqlparse_js
+
+## Example:
+
+```python
+from cratedb_sqlparse import sqlparse
+
+query = """
+    SELECT * FROM SYS.SHARDS;
+    INSERT INTO doc.tbl VALUES (1);
+"""
+statements = sqlparse(query)
+
+select_query = statements[0]
+
+print(select_query.query)
+# 'SELECT * FROM SYS.SHARDS'
+```
+
+## Limitations
+
+Listeners are not implemented, which means that you can only: Validate SQL syntax,
+split queries and get some Tokens metadata from
+the query, if you need some more information like what https://github.com/macbre/sql-metadata does (
+e.g. get the columns of this query) open a new issue.
+
+New features should preferably be implemented in all available targets.
+
+## Adding a new target
+
+The target language has to be available in antlr4,
+see https://github.com/antlr/antlr4/blob/master/doc/targets.md.
+
+Add the new target and paths to the build script, see `setup_grammar.py`.
+
+There are several features that would need to be implemented, like case-insensitive input stream, native
+exceptions as error listener, dollar strings and any new one. See past commits to see how they were
+implemented in Python and Javascript, remember that CrateDB's SQLParser written in Java is the most
+complete and the default reference.
+
+## Building locally & using a different CrateDB version.
+
+The generated parser is not uploaded to the repository since it's huge, to use the package locally or
+to build a different version use the build script.
+
+At the end of the build script `setup_grammar.py` the target and the versions can be modified.
+
+The script needs two dependencies `pip install antlr4-python3-runtime requests` you can either
+install those manually or use the `pyproject.toml` from the python target, both options can be used to build targets.
+
+```python
+if __name__ == '__main__':
+    version = '5.6.4'
+    target = Antlr4Target.python
+    download_cratedb_grammar(version)
+    compile_grammar(target)
+    patch_lexer(target)
+    set_version(target, version)
+```

setup_grammar.py

@@ -123,8 +123,11 @@ def set_version(target: Antlr4Target, version: str):
     with open(target_path / index_file, "a") as f:
         f.write(f"{variable} = {version}\n")
 
-# if __name__ == '__main__':
-#     download_cratedb_grammar('5.6.4')
-#     compile_grammar(Antlr4Target.js)
-#     patch_lexer(Antlr4Target.js)
-set_version(Antlr4Target.js, '5.45.4')
+
+if __name__ == '__main__':
+    version = '5.6.4'
+    target = Antlr4Target.python
+    download_cratedb_grammar(version)
+    compile_grammar(target)
+    patch_lexer(target)
+    set_version(target, version)