update test cases
add an interface to describe how to map program elements between two consecutive versions
make IProgramElementMapper provide a method to set up
implement a mapping algorithm of tokens with traditional unix diff
add a class to compare tokens with the values
make TraditionalDiffTokenMapper use Equalizer of tokens
change default equals method of token from that based on values to that based on position
modify hashCode of token to fit the new equals algorithm
modify hashCode of token to fit the new equals algorithm
implement comparator for token
tested TraditionalDiffTokenMapper