Implement flags

[Pedro Ramalho]

There are numerous flags that must be added to CACTI in order to customize it's usage:

• -vi, verbose idempotency
• -vc, verbose correctness
• -CXX, specify standard to test
• -itX, specify the maximum number of idempotency tries
• -OX, specify the optimization flag to be used in the emit_llvm() command

Some other flags may be implemented as well.