Integration edits for repo:voltha-docs use.

This patch will add makefile targets and exclusions for doc8 (estructuredText) linting.

makefiles/lint/doc8/excl.mk
makefiles/lint/doc8/doc8.mk
makefiles/lint/doc8/help.mk
makefiles/lint/doc8/include.mk
makefiles/lint/doc8/install.mk
------------------------------
  o Apply exclusion list so checking will not fail on python venv dirs.
  o Split include.mk into named modular makfiles.

makefiles/lint/include.mk
makefiles/lint/shell.mk
-------------------------
  o Remove legacy shell.mk config, lint target loads from lint/shell/*.

Change-Id: I8c214dc499356edf9778ae7ec1deeddf35bd3b65
diff --git a/makefiles/lint/doc8/help.mk b/makefiles/lint/doc8/help.mk
new file mode 100644
index 0000000..1ec6cb8
--- /dev/null
+++ b/makefiles/lint/doc8/help.mk
@@ -0,0 +1,46 @@
+# -*- makefile -*-
+# -----------------------------------------------------------------------
+# Copyright 2022-2023 Open Networking Foundation (ONF) and the ONF Contributors
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+# -----------------------------------------------------------------------
+
+$(if $(DEBUG),$(warning ENTER))
+
+## -----------------------------------------------------------------------
+## Intent: Display topic help
+## -----------------------------------------------------------------------
+help-summary ::
+	@printf '  %-30s %s\n' 'lint-doc8'\
+      'Style check ReStructed Text (rst) documents'
+	@printf '  %-30s %s\n' 'lint-doc8-help'\
+	  'Show verbose target help'
+  ifdef VERBOSE
+	@$(MAKE) --no-print-directory lint-doc8-help
+  endif
+
+## -----------------------------------------------------------------------
+## Intent: Display extended topic help
+## -----------------------------------------------------------------------
+.PHONY: lint-doc8-help
+lint-doc8-help ::
+	@printf '  %-30s %s\n' 'lint-doc8-all'\
+	  'Doc8 check available sources'
+	@printf '  %-30s %s\n' 'lint-doc8-mod'\
+	  'Doc8 check locally modified files (git status)'
+#	@printf '  %-30s %s\n' 'lint-doc8-src'\
+#	  'Doc8 check files by path'
+
+$(if $(DEBUG),$(warning LEAVE))
+
+# [EOF]