Clean up the new improvements to Appveyor build.

We do not use the powershell script install_python.ps1 anymore since we use the miniconda preinstalled on the appveyor VM.

README.rst

@@ -167,7 +167,7 @@ Release history
 ----------------------
 
 Version 0.7.5 (released July 2019)
-    Bug fix
+    Bug fixes and improvements to continuous integration
 
 Version 0.7.4 (released June 2019)
     New flexible solver for 1D advection-diffusion processes on non-uniform grids, along with some bug fixes.

appveyor.yml

@@ -1,43 +1,34 @@
 # CI on Windows via appveyor
-# This file is based on xarray, which is in turn based on
-# Olivier Grisel's python-appveyor-demo
-branches:
-  except:
-    - fix-docs
+# branches:
+#   except:
+#     - fix-docs
 
 # Build worker image (VM template)
 image: Visual Studio 2017
 
 environment:
-
+  # Use the same root miniconda for all builds...
+  # The build itself happens in a custom conda environment
   matrix:
     - PYTHON: "C:\\Miniconda36-x64"
-      #PYTHON_VERSION: "3.6"
-      PYTHON_ARCH: "64"
       CONDA_ENV: "py36-windows"
     - PYTHON: "C:\\Miniconda36-x64"
-      #PYTHON_VERSION: "3.7"
-      PYTHON_ARCH: "64"
       CONDA_ENV: "py37-windows"
 
 install:
-  # Install miniconda Python
-  #- "powershell ./ci/install_python.ps1"
-
-  # Prepend newly installed Python to the PATH of this build (this cannot be
-  # done from inside the powershell script as it would require to restart
-  # the parent CMD process).
+  # Prepend the Miniconda to the PATH of this build
   - "SET PATH=%PYTHON%;%PYTHON%\\Scripts;%PATH%"
-
-  # install xarray and dependencies
-  #- "conda init cmd.exe"
+  # Use the latest conda version
   - "conda update --yes conda"
+  # Set up, activate, and list the specific build/test environment
   - "conda env create --file ./ci/requirements-%CONDA_ENV%.yml"
   - "activate test_env"
   - "conda list"
+  # Build and install into custom environment
   - "python -m pip install . --no-deps -vv"
 
 build: false
 
 test_script:
+  # Run the full test suite
   - "pytest --pyargs climlab.tests --verbose"