Refactor JSON::Ext::Parser to split configuration and parsing state

Ref: ruby#718

The existing `Parser` interface is pretty bad, as it forces to
instantiate a new instance for each document.

Instead it's preferable to only take the config and do all the
initialization needed, and then keep the parsing state on the
stack on in ephemeral memory.

This refactor makes the `JSON::Coder` pull request much easier to
implement in a performant way.

Co-Authored-By: Étienne Barrié <[email protected]>

Rakefile

@@ -40,8 +40,8 @@ EXT_GENERATOR_DL  = "#{EXT_GENERATOR_DIR}/generator.#{CONFIG['DLEXT']}"
 EXT_GENERATOR_SRC = "#{EXT_GENERATOR_DIR}/generator.c"
 
 JAVA_DIR            = "java/src/json/ext"
-JAVA_RAGEL_PATH     = "#{JAVA_DIR}/Parser.rl"
-JAVA_PARSER_SRC     = "#{JAVA_DIR}/Parser.java"
+JAVA_RAGEL_PATH     = "#{JAVA_DIR}/ParserConfig.rl"
+JAVA_PARSER_SRC     = "#{JAVA_DIR}/ParserConfig.java"
 JAVA_SOURCES        = FileList["#{JAVA_DIR}/*.java"]
 JAVA_CLASSES        = []
 JRUBY_PARSER_JAR    = File.expand_path("lib/json/ext/parser.jar")
@@ -95,9 +95,9 @@ end
 file JAVA_PARSER_SRC => JAVA_RAGEL_PATH do
   cd JAVA_DIR do
     if RAGEL_CODEGEN == 'ragel'
-      sh "ragel Parser.rl -J -o Parser.java"
+      sh "ragel ParserConfig.rl -J -o ParserConfig.java"
     else
-      sh "ragel -x Parser.rl | #{RAGEL_CODEGEN} -J"
+      sh "ragel -x ParserConfig.rl | #{RAGEL_CODEGEN} -J"
     end
   end
 end