Use truth table into spec

When running the experiment, we found the synthesis time is unstable across different mutations even if we have already set the slv-seed. One initial idea to solve this issue is to create a truth table to replace the spec file. 

To be specific, we will replace y = x + 1 by if (x == 0) {y = 1} elif (x == 1) {y =2 }... so that all mutations will have one same spec format.