Changed compiler class and implemented 5 commands
AsmJit::Compiler was changed to AsmJit::Assembler because
this class gives more low-level access (for example to registers).
Fixed print functions (they spoiled top of the stack). Implemented
for new commands. First - top (printing top of the stack without
pop), second - push (pushing constant to the stack). Other -
calculating commands: add, sub, mul.