Implement missing Python calls to make Pandas usage natural

[liuliu]

This PR added implementation for PyObject_RichCompare, PyNumber_Invert,
PyNumber_And, PyNumber_Or such that the usual filtering with in pandas
would be more natural. Previously, if you do:

let pd = Python.import("pandas")
let df = pd.read_csv("a.csv")
print(df[df["column"] == match])

Will error, because we only implemented PyObject_RichCompareBool, and it
will return a simple boolean, rather than a complex PyObject for
querying. By implementing PyObject_RichCompare, PyNumber_Invert,
PyNumber_And and PyNumber_Or, I believe we enabled full range of Pandas'
filtering short-hand now:

let pd = Python.import("pandas")
let df = pd.read_csv("a.csv")
print(df[~((df["column"] == match) | (df["year"] < this_year))])

I double checked Swift type inference. If you just do:

if onePythonObject == anotherPythonObject {
}

The type system will still choose the right PyObject_RichCompareBool function.
The confusion only happens if you do:

let result = onePythonObject == anotherPythonObject

and you can workaround this by providing explicit type. I think this is a small
price to pay to enable a capable library such as Pandas usable within Swift.

[pvieito]

@compnerd Hi! As this is a source-breaking change I think it would be important to have it reviewed by the Swift for TensorFlow team.

[liuliu]

Thanks @pvieito @compnerd ! If we worried about ongoing source-breaking changes in the future, maybe we should review all Number Protocol: https://docs.python.org/3/c-api/number.html and decide what we should port over what we shouldn't? I can see some cases %, @ and ** is desirable, some of these will not conflict with Swift: https://docs.swift.org/swift-book/LanguageGuide/AdvancedOperators.html (~, |, ^, &).

[saeta]

Thanks for flagging this @pvieito ! I defer to @marcrasi for a more detailed review, but based on my quick look over, this seems good to me. Thanks for this @liuliu!

[liuliu]

Thanks @marcrasi ! Before check in, do you want me to add the rest: InplaceXor, Xor, InplaceAnd, InplaceOr?

[marcrasi]

Thanks @marcrasi ! Before check in, do you want me to add the rest: InplaceXor, Xor, InplaceAnd, InplaceOr?

Yeah, that sounds like a good idea!

[liuliu]

Done!