Update android ndk to r17c and update documentation

Author: opacam

Dockerfile

@@ -26,7 +26,7 @@ RUN apt -y update -qq \
 
 
 ENV ANDROID_NDK_HOME="${ANDROID_HOME}/android-ndk"
-ENV ANDROID_NDK_VERSION="16b"
+ENV ANDROID_NDK_VERSION="17c"
 ENV ANDROID_NDK_HOME_V="${ANDROID_NDK_HOME}-r${ANDROID_NDK_VERSION}"
 
 # get the latest version from https://developer.android.com/ndk/downloads/index.html
@@ -97,7 +97,7 @@ RUN dpkg --add-architecture i386 \
         build-essential ccache git python2.7 python2.7-dev \
         libncurses5:i386 libstdc++6:i386 libgtk2.0-0:i386 \
         libpangox-1.0-0:i386 libpangoxft-1.0-0:i386 libidn11:i386 \
-        zip zlib1g-dev zlib1g:i386 \
+        libffi-dev zip zlib1g-dev zlib1g:i386 \
     && apt -y autoremove \
     && apt -y clean
 

doc/source/quickstart.rst

@@ -93,11 +93,34 @@ named ``tools``, and you will need to run extra commands to install
 the SDK packages needed. 
 
 For Android NDK, note that modern releases will only work on a 64-bit
-operating system. If you are using a 32-bit distribution (or hardware),
-the latest useable NDK version is r10e, which can be downloaded here:
+operating system. The minimal, and recommended, NDK version to use is r17c:
+
+ - `Linux (64-bits) <https://dl.google.com/android/repository/android-ndk-r17c-linux-x86_64.zip>`_
+ - `Macos X (64-bits) <https://dl.google.com/android/repository/android-ndk-r17c-darwin-x86_64.zip>`_
+ - Windows users should create a virtual machine with an GNU Linux os
+   installed, and then you can follow the described instructions from within
+   your virtual machine.
+
+.. note::
+    Versions below r17 may cause troubles while compiling some recipes. Our
+    tests had been done against ndk versions r17b and r17c. Later versions of
+    the android ndk still are not proved to work with python-for-android, and
+    may work or not...so...better to stick to the recommended version (r17c).
+
+If you are using a 32-bit distribution (or hardware),
+the latest usable NDK version is r10e, which can be downloaded here:
 
 - `Legacy 32-bit Linux NDK r10e <http://dl.google.com/android/ndk/android-ndk-r10e-linux-x86.bin>`_
 
+.. warning::
+    **32-bit distributions**
+
+    Since the python2 recipe updated to version 2.7.15, the build system has
+    been changed and you should use an old release of python-for-android, which
+    contains the legacy python recipe (v2.7.2). The last python-for-android
+    release with the legacy version of python is version
+    `0.6.0 <https://github.com/kivy/python-for-android/archive/0.6.0.zip>`_.
+
 First, install a platform to target (you can also replace ``19`` with
 a different platform number, this will be used again later)::
 
@@ -113,7 +136,7 @@ Then, you can edit your ``~/.bashrc`` or other favorite shell to include new env
 
     # Adjust the paths!
     export ANDROIDSDK="$HOME/Documents/android-sdk-21"
-    export ANDROIDNDK="$HOME/Documents/android-ndk-r10e"
+    export ANDROIDNDK="$HOME/Documents/android-ndk-r17c"
     export ANDROIDAPI="26"  # Target API version of your application
     export NDKAPI="19"  # Minimum supported API version of your application
     export ANDROIDNDKVER="r10e"  # Version of the NDK you installed