Build process #160

Hello.

I am trying to build QPython from sources and I have some questions.

In order to get something to work I had to install old versions of all the build software. Here is what I came up with:

• gradle 4.10.1
• Android SDK from Android studio.
• Android NDK r16 (Dec 2018).
• Replace path to SDK in local.properties file.
• Replace target ABI from armeabi to armeabi-v7a in every build.gradle and Application.mk file.
• Add missing #include <string.h> in every *.cpp file that uses strerror function.
• Add

  lintOptions {
      abortOnError false
  }
  

  to some build.gradle files.

After all that I finally managed to get gradle build working and I got 2 APK files (debug and release). But I can't install them on my machine, because they both are unsigned (I get signature missing error by running adb install qpython-release-unsigned.apk).

So here are my questions:

1. How can I sign result APKs? And why isn't this process included in gradle build?
2. Is there any build instruction? Could I avoid all that hustle I described in the list above?
3. (Most important for me) Can I build this for x86_64 architecture?