* A_Instruction, C_Instruction and M_Instruction renamed to *_extension
* These files decode and executes extensions
* These classes use a new base clase extension_base
* Execute & Instruction classes heavyly modified:
* Execute now is BASE_ISA and decodes and executes base ISA, Zicsr & Zifencei
* Instruction keeps the instruction being executed, nothing else
* Add memory interface to ISS to clear the code and the structure
* Removed "using namespace " directives, all classes are called using their namespace
* Added proper header to each file
* Added license to all files
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