Rst docs conversion (#3496)

Rst docs conversion

docs/source/appendix/CHAPTER_Auxprogs.rst

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+Auxiliary programs
+==================
+
+Besides the main yosys executable, the Yosys distribution contains a set of
+additional helper programs.
+
+yosys-config
+------------
+
+The yosys-config tool (an auto-generated shell-script) can be used to query
+compiler options and other information needed for building loadable modules for
+Yosys. See Sec. \ :numref:`chapter:prog` for details.
+
+.. _sec:filterlib:
+
+yosys-filterlib
+---------------
+
+The yosys-filterlib tool is a small utility that can be used to strip or extract
+information from a Liberty file. See :numref:`Sec. %s <sec:techmap_extern>` for
+details.
+
+yosys-abc
+---------
+
+This is a fork of ABC with a small set of custom modifications that have not yet
+been accepted upstream. Not all versions of Yosys work with all versions of ABC.
+So Yosys comes with its own yosys-abc to avoid compatibility issues between the
+two.