2.1.0

Added

• Add tokens for 3DM, 3DZ, and 4D coordinates to Lexer.
• Method Lexer::value() to get current token value.
• Match Z, M, or ZM tokens in Parser (not currently used).
• Add test for Parser reuse.
• Add test for Lexer reuse.

Changed

• Regex used to catch tokens.
• Allow Lexer instantiation with no parameters so object can be reused.
• Allow Parser instantiation with no parameters so object can be reused.
• Changed visibility of Parser::$type.
• Use Lexer::value() in Parser.
• Set srid to null before parsing value.
• Consolidated all Parser test data into ParserTest.
• Update usage documentation in README.md.