doc: use minimal conda environment to build

.readthedocs.yml

@@ -0,0 +1,5 @@
+python:
+  version: 3
+  pip_install: false
+conda:
+  file: conda/artiq-doc.yml

conda/artiq-doc.yml

@@ -0,0 +1,14 @@
+# conda description for an environment to build artiq documentation
+# $ conda env create -f conda/artiq-doc.yml
+name: artiq-doc
+channels:
+  - m-labs/label/dev
+  - m-labs/label/main
+  - defaults
+dependencies:
+  - python 3.5.2
+  - sphinx 1.4.8
+  - sphinx-argparse
+  - sphinxcontrib-wavedrom
+  - sphinx_rtd_theme
+  - pythonparser 1.0

doc/manual/requirements.txt

@@ -1,4 +0,0 @@
-sphinx_rtd_theme
-sphinx-argparse
-sphinxcontrib-wavedrom
-pythonparser