Initial implementation of lpython builtin module

[namannimmo10]

Originally taken from #1 (comment)

[certik]

Call it lpython_builtin.py.

[certik]

Now we need to import this automatically when chr is encountered in AST to ASR and call it.

[certik]

That looks good. The tests fail, so that needs to be fixed.

[certik]

The load_module function has to accept the main (global) TranslationUnit and it will use it to:

• on "import A" it will lookup the global TranslationUnit for a module A and use it (construct ExternalSymbols from it), otherwise it will recursively call itself to import A, and then use it
• Once it's done importing a given module, it will save it to the global TranslationUnit

Let's open up a new issue for this.

[certik]

It should work now. The strings in ord and chr are not always implemented in the LLVM backend, so we can't actually run it, but the ASR looks pretty good. I need to implement some intrinsic function that actually works in LLVM, then we can properly test it.

[certik]

I implemented abs() to load our own function. It seems to work now. The compile time value is not implemented yet, we'll do it in a subsequent PR. Finally, we really have to refactor this to follow LFortran's design.

[namannimmo10]

I think this should be ready to go in -- we can complete the remaining tasks in upcoming PRs. Thanks for working on it with me

[certik]

This approach now needs to be refactored like in LFortran.