produce built docs in build/docs rather than docs/build

* build docs in a tmpdir to allow independant docs builds
* you can now run `tox -e documentation,py38-test-dev ldaptor.test.test_usage` and check-manifest passes

Author: graingert

.gitignore

@@ -4,7 +4,6 @@ _trial_temp/
 ldaptor.test.*/
 ldaptor/test/ldif/webtests.tmp
 docs/*.png
-docs/build/
 ldaptor.egg-info
 .idea
 .coverage

CONTRIBUTING.rst

@@ -64,7 +64,7 @@ Building the documentation
 --------------------------
 
 The documentation is managed using Python Sphinx and is generated in
-docs/build.
+build/docs.
 
 There is a helper to build the documentation using tox ::
 

pyproject.toml

@@ -73,10 +73,12 @@ commands =
 [testenv:documentation]
 deps = sphinx
 basepython=python3.8
+changedir = {envtmpdir}
+whitelist_externals = cp
 commands =
-    mkdir -p docs/build
-    sphinx-build -b html -Ean -j 2 -w build/sphinx-errors \
-        docs/source docs/build
+    sphinx-build -b html -Ean -j 2 -w sphinx-errors \
+        {toxinidir}/docs/source ./docs/
+    cp -r . {toxinidir}/build
 
 [testenv:release]
 deps = pep517