Additional operators for symbolic evaluation

[balasub]

The following operators are missing from symbolic evaluation in OpLibrary.cs.

GCD
GCDAll
Impl
IsSubstring
LCM
LCMAll
LstLength
LstReverse
MaxAll
Min
MinAll
Mod
Neg
Not
NotImplemented
Or
OrAll
Prod
Qtnt
Relabel
Sign
StrAfter
StrBefore
StrFind
StrGetAt
StrJoin
StrLength
StrLower
StrReplace
StrReverse
StrUpper
ToList
ToNatural
ToOrdinal
ToString
ToSymbol

[balasub]

Support for Or, OrAll, MaxAll, Min, and MinAll added in 3be10ce. The remaining missing operators are now:

GCD
GCDAll
Impl
IsSubstring
LCM
LCMAll
LstLength
LstReverse
Mod
Neg
Not
NotImplemented
Prod
Qtnt
Relabel
Sign
StrAfter
StrBefore
StrFind
StrGetAt
StrJoin
StrLength
StrLower
StrReplace
StrReverse
StrUpper
ToList
ToNatural
ToOrdinal
ToString
ToSymbol