First cut at Hypergeometric2F1 and some other Hypergeometric function revisions (#1431)

In addition to adding Hypergeometric2F1, we start moving code to `mathics.eval.specialfns.hypergeom`

Fixes #1187 
 
Most of the eval functions have been moved out of `mathics.builtin.specialfns.hypergeom`. And in the process, we expand hyper results to match what WMA does more closely. Some prior erroneous evaluation was therefore corrected.

However, this PR is already large, so Hypergeometric2U will be handled separately.

Moving eval code for `MeijerG`, was attempted, but that causes a weird interaction with `test/doc/doc_common.py`, which somehow makes it think that hypergeom is included more than once.

---------

Co-authored-by: Aravindh Krishnamoorthy <aravindh.krishnamoorthy@fau.de>

Author: rocky

CHANGES.rst

@@ -9,6 +9,7 @@ New Builtins
 
 * ``$SessionID``
 * ``BinaryReadList``
+* ``Hypergeometric2F1``
 
 Internals
 ---------
@@ -17,6 +18,19 @@ Mathics scanner exceptions of class TranslateError are incompatible
 with previous versions, and now store error parameters, "name", "tag", and
 "args".
 
+WMA Compatibility
+-----------------
+
+Hypergeometric functions have been revised to conform better to WMA behavior by
+expanding hypergeometric results.
+
+Bugs
+----
+
+* Fixed #1187
+
+
+
 8.0.1
 -----
 

mathics/builtin/messages.py

@@ -192,6 +192,7 @@ class General(Builtin):
         "fnsym": (
             "First argument in `1` is not a symbol " "or a string naming a symbol."
         ),
+        "hdiv": "`1` does not exist. Arguments are not consistent.",
         "heads": "Heads `1` and `2` are expected to be the same.",
         "ilsnn": (
             "Single or list of non-negative integers expected at " "position `1`."