Bug fix with shifts, instruction parsing and Open File

• Files are ready to be ran when opened.
• Instruction parsing has been refactored and should be more rigorous. Some weird cases like BLS (which is B + LS and not BL + S) or STRHS (str + hs and not strh + s) should not cause problems anymore.
• Errors on immediate value of shift instruction should now be correctly detected. A lot more checks of errors in code in general.
• Fix errors on hex generation of extra memory instruction and shift instruction. Same for data proc and memory instruction with shifts.