refactoring of BlockParser#select_leaf_type()

The generation of MatchData objects will be reduced by this change.
renamed constants used in BlockParser#slect_leaf_type()
renamed local variables in BlockParser.assign_head_re appropriately
refactoring of BlockParser.assign_head_re()
refactoring of BlockParser#select_leaf_type()
changed the order of evaluating regular leafs in BlockParser#assign_head_re()
Merge changes that are made between 0.0.0.13.develop and 0.0.0.14.develop
update the version number to 0.0.2: merged changes that were made between 0.0.0.13.develop and 0.0.0.14.develop