refactoring of SiPLE's parser

[christoff-buerger]

The parser of the SiPLE example is rather old; better best practices for manual parser implementation have been applied for example for the binary-numbers, internal RACR AST specification and ttc-2015-fuml-activity-diagrams parsers. SiPLE's parser has to be refactored accordingly.

This task may require to make all these parsers more consistent in terms of a general parser combinator library or at least common parsing support functions.

[christoff-buerger]

The issue is related to issue #42.

[christoff-buerger]

The parser should be refactored after issue #42 is solved to benefit from improved AST constructor functions (:ASTType functions).