Doc code revision order1 (Mathics3#986)

Another round of incremental changes. This branch requires small tweaks
in mathics-django to keep compatibility (just about the names of certain
properties in the documentation classes)
* Start adding pytests for LaTeX documentation.
* Fix `mathics.doc.Documentation` class, which seems to be mixed and
smashed with the `DocChapter` class in an old merge.
* Split the part of the code associated with `mathics.doc.Documentation`
which does not depend on the `mathics.builtin` code, which was moved to
`mathics.doc.MathicsMainDocumentation`.
* Small tweaks and reorganization to make the code closer to the
@rocky's branch `doc-code-revision`.
* Classes that are not used like `LaTeXDocumentation` were removed.
* Tweaks to make the LaTeX documentation to compile

mathics/builtin/trace.py

@@ -446,8 +446,9 @@ class PythonCProfileEvaluation(Builtin):
       <dd>profile $expr$ with the Python's cProfiler.
     </dl>
 
-    >> PythonCProfileEvaluation[a + b + 1]
-     = ...
+    ## This produces an error in the LaTeX documentation.
+    ## >> PythonCProfileEvaluation[a + b + 1]
+    ##  = ...
     """
 
     attributes = A_HOLD_ALL_COMPLETE | A_PROTECTED

mathics/core/load_builtin.py

@@ -8,6 +8,7 @@
 
 import importlib
 import inspect
+import logging
 import os
 import os.path as osp
 import pkgutil
@@ -144,6 +145,12 @@ def import_and_load_builtins():
     """
     Imports Builtin modules in mathics.builtin and add rules, and definitions from that.
     """
+    # TODO: Check if this is the expected behavior, or it the structures
+    # must be cleaned.
+    if len(mathics3_builtins_modules) > 0:
+        logging.warning("``import_and_load_builtins`` should be called just once...")
+        return
+
     builtin_path = osp.join(
         osp.dirname(
             __file__,

mathics/data/ExampleData/EinsteinSzilLetter.txt

@@ -67,4 +67,3 @@ is now being repeated.
 Yours very truly,
 A. Einstein
 (Albert Einstein)
-

mathics/data/ExampleData/Middlemarch.txt

@@ -293,4 +293,4 @@ going about what work he had in a mood of despair, and Rosamond
 feeling, with some justification, that he was behaving cruelly.  It was
 of no use to say anything to Tertius; but when Will Ladislaw came, she
 was determined to tell him everything.  In spite of her general
-reticence, she needed some one who would recognize her wrongs.
+reticence, she needed some one who would recognize her wrongs.