Add missing builtins

[davidar]

I added a bunch of WMA builtins that aren't in Mathics yet:

• NumberDigit
• BellB
• EulerE
• JacobiSymbol
• KroneckerSymbol
• LucasL
• PolygonalNumber
• SquaresR
• LinearRecurrence
• RootSum I think this one needs some more work for converting to sympy
• SeriesCoefficient
• DivisorSigma
• DivisorSum
• IntegerPart
• IntegerPartitions
• MersennePrimeExponent
• MoebiusMu
• PowersRepresentations
• HypergeometricU
• LambertW
• Subfactorial
• PolyLog
• ReverseSort

I also expanded the functionality of a few existing builtins to match the behaviour of WMA:

• handle non-integer bounds in Sum
• fixed a bug in RealDigits where it would report the wrong number of digits for powers of 10 (or whatever base is specified)
• support Fibonacci polynomials
• support symbolic bounds in Table (and other IterationFunctions)
• support providing SeriesData to CoefficientList
• added the listable attribute to a few functions
• allow supplying a precision when calling N[] on a complex number

I can split some of these out into separate PRs if they need more work to merge.

I've started setting up some automated tests to pull all the Mathematica programs listed in OEIS and check that Mathics can evaluate them to the correct sequence values - these are all just the low hanging fruit that fell out of doing that for the first couple of hundred sequences.

[rocky]

Wow - thanks. I'll try to look at over the weekend.

[rocky]

Ok, in that case, keep what indicates your version.

Ultimately it would be ideal if we could start noting somewhere (if this doesn't already exist), the differences between versions so that someone might start a "version compatibility" package. Then packages that are written for a specific version would work.

[mmatera]

Maybe just adding a comment above the attribute definition, inside the class?

[davidar]

I split out the major groups of changes into separate PRs as suggested: #1134, #1135, #1136

[rocky]

LGTM