ENH: Add manylinux-build-wheels script

## Step 1: Download dockcross/manylinux-x64

```
docker pull dockcross/manylinux-x64
docker run dockcross/manylinux-x64 > ~/bin/dockcross-manylinux-x64
chmod u+x ~/bin/dockcross-manylinux-x64
```


##  Step 2: Build wheels

```
git clone git://github.com/jcfr/SimpleITKPythonPackage.git
cd SimpleITKPythonPackage
dockcross-manylinux-x64 ./scripts/manylinux-build-wheels.sh
```

Author: jcfr

scripts/manylinux-build-wheels.sh

@@ -0,0 +1,30 @@
+#!/bin/bash
+set -e -x
+
+# Build standalone project and populate archive cache
+mkdir -p /work/standalone-build
+pushd /work/standalone-build > /dev/null 2>&1
+  cmake -DSimpleITKPythonPackage_BUILD_PYTHON:PATH=0 -G Ninja ../
+  ninja
+popd > /dev/null 2>&1
+
+# Compile wheels re-using standalone project and archive cache
+for PYBIN in /opt/python/*/bin; do
+    if [[ ${PYBIN} == *"cp26"* ]]; then
+        echo "Skipping ${PYBIN}"
+        continue
+    fi
+    ${PYBIN}/pip install --user -r /work/requirements-dev.txt
+    ${PYBIN}/python setup.py bdist_wheel -- \
+      -DSimpleITK_DIR:PATH=/work/standalone-build/SimpleITK-superbuild/SimpleITK-build \
+      -DSWIG_EXECUTABLE:PATH=/work/standalone-build/SimpleITK-superbuild/Swig/bin/swig
+    ${PYBIN}/python setup.py clean
+done
+
+# Since there are no external shared libraries to bundle into the wheels
+# this step will fixup the wheel switching from 'linux' to 'manylinux1' tag
+for whl in dist/*.whl; do
+    auditwheel repair $whl -w /work/dist/
+    rm $whl
+done
+