[feature request] Ability to execute the code without compiling using llvm JIT

[Vipul-Cariappa]

It would be very useful if we could directly execute the lpython code without compiling it using the llvm JIT. It will prevent the creation of *.tmp.o and the executable files.

The main idea is to run lpython --jit program.py

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I have a working implementation ready. If this is useful I could open a PR.