Build Python wheels for windows on travis (#160)

* upgrade for windows on travis

* Install python on travis windows, update readme, update tests

* update readme, travis config and clean code

* install python inside cibuildwheel run

* use register to get python path

* fixes from review

* fix pip version

* use nuget for instal python

* clean code

* Update cibuildwheel/windows.py

Co-Authored-By: Joe Rickerby <joerick@mac.com>

* fixes from review

* Final bits of tidy up

README.md

@@ -14,13 +14,15 @@ What does it do?
 
 |   | macOS 10.6+ | manylinux i686 | manylinux x86_64 |  Windows 32bit | Windows 64bit |
 |---|---|---|---|---|---|
-| Python 2.7 | ✅ | ✅ | ✅ | ✅  | ✅  |
-| Python 3.4 | ✅ | ✅ | ✅ | ✅* | ✅* |
+| Python 2.7 | ✅ | ✅ | ✅ | ✅² | ✅² |
+| Python 3.4 | ✅ | ✅ | ✅ | ✅¹²| ✅¹²|
 | Python 3.5 | ✅ | ✅ | ✅ | ✅  | ✅  |
 | Python 3.6 | ✅ | ✅ | ✅ | ✅  | ✅  |
 | Python 3.7 | ✅ | ✅ | ✅ | ✅  | ✅  |
 
-> \* Not supported on Azure Pipelines
+> ¹ Not supported on Azure Pipelines 
+>
+> ² Not supported on Travis
 
 - Builds manylinux, macOS and Windows (32 and 64bit) wheels using Azure Pipelines, Travis CI, AppVeyor, and CircleCI
 - Bundles shared library dependencies on Linux and macOS through [auditwheel](https://github.com/pypa/auditwheel) and [delocate](https://github.com/matthew-brett/delocate)
@@ -34,7 +36,7 @@ Usage
 |                 | Linux | macOS | Windows |
 |-----------------|-------|-------|---------|
 | Azure Pipelines | ✅    | ✅    | ✅      |
-| Travis CI       | ✅    | ✅    |         |
+| Travis CI       | ✅    | ✅    | ✅     |
 | AppVeyor        |       |       | ✅      |
 | CircleCI        | ✅    | ✅    |         |
 
@@ -101,11 +103,12 @@ jobs:
     <summary><b>Travis CI</b>
         <img width="16" src="https://unpkg.com/simple-icons@latest/icons/apple.svg" />
         <img width="16" src="https://unpkg.com/simple-icons@latest/icons/linux.svg" />
+        <img width="16" src="https://unpkg.com/simple-icons@latest/icons/windows.svg" />
     </summary>
 
 - To build Linux and Mac wheels on Travis CI, create a `.travis.yml` file in your repo.
 
-    ```
+    ```yaml
     language: python
     
     matrix:
@@ -123,6 +126,18 @@ jobs:
       - cibuildwheel --output-dir wheelhouse
     ```
 
+  To build on Windows too, add this matrix entry: 
+  ```yaml
+    - os: windows
+      language: shell
+      before_install:
+       - choco install python3 --version 3.6.8 --no-progress -y
+      env:
+       - PATH=/c/Python36:/c/Python36/Scripts:$PATH
+  ```
+
+  Note that building Windows Python 2.7 wheels on Travis is unsupported.
+
   Then setup a deployment method by following the [Travis CI deployment docs](https://docs.travis-ci.com/user/deployment/), or see [Delivering to PyPI](#delivering-to-pypi) below.
 
 </details>