Add `normalize!` and `normalize`

This would take an `AbstractCIGAR` and return a new one of the same type where

* All `OP_P` is removed
* `OP_H` is replaced by `OP_S`
* `OP_Eq` and `OP_X` is replaced by `OP_M`
* All consecutive ops of the same operation are collapsed

Note the order in which these ops happens is significant