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 the changes for version 0.0.0.13.develop and changes that improve the performance for Ruby >= 1.9.3