Make it easier to build Mathics

Allow more packages to be optional.
Doc a little more in doc/doc.py

Author: rocky

mathics/doc/doc.py

@@ -1,4 +1,14 @@
 # -*- coding: utf-8 -*-
+"""
+A module which extracts LaTeX, XML documentation from documentation/*.mdoc and from Mathics modules.
+It also extracts doctests as well.
+
+Running LaTeX, or the tests is done elsewhere, as is viewing extracted XML docs.
+
+See also `../test.py` for a command-line interface that calls this.
+
+This code should be replaced by sphinx and autodoc.
+"""
 
 from html import escape as html_escape
 import re

requirements-dev.txt

@@ -1,3 +1,8 @@
+# Optional packages which add functionality or speed things up
+scikit-image # FindMinimum can use this
+lxml  # for HTML parsing used in builtin/fileformats/html
+wordcloud # Used in builtin/image.py by WordCloud()
+
 # Additional packages used in testing
 pytest
 pytest-xdist

setup.py

@@ -100,11 +100,9 @@ def read(*rnames):
     "psutil",  # for $SystemMemory
     "llvmlite",
     "requests",
-    "scikit-image",
-    "wordcloud",  # Used in builtin/image.py by WordCloud()
-
-    # lxml is an optional dependency for HTML parsing
-    # "lxml", # Used in builtin/fileformats/html
+    # lxml is an optional dependency for HTML parsing used in builtin/fileformats/html
+    # "scikit-image", optional
+    # "wordcloud",  # Used in builtin/image.py by WordCloud()
 ]