Transition from AYACC/ALEX to Flex/Bison

EaseaLex.l and EaseaParse.y are now Flex and Bison compliant, and generate normally the same code as with alex and ayacc.

This change is a bug for bug change : if a bug was on the code of EaseaLex.l or EaseaParse.y, the same bug will appear (but it will be easier to debug it with Flex and Bison).

resolve #5 .