Add android platform support

[i25ffz]

The android/ directory contains android ndk-build dependent files:
-config.h Configuration options for android arm platform
-speex_config_types.h Configuration options for android arm platform
-jni Build script for android ndk-build

Just need run cmd: cd android && ndk-build

[erikd]

Seems sensible to me. Travis build is find. Appveyor seems to be complaining about MSVC project files which has nothing to do with this submission.

[i25ffz]

Seems the porting don't change any files related MSVC project.

[i25ffz]

Porting steps:

1. Run configure got the config.h header files for android platform;
2. Add android ndk needed makefile script & jni file.

TODO:

1. Add android x86 arch support.

[stephengroat]

if this is integrated, i could also add ndk builds to travis

[i25ffz]

yes, it is integrated for android platform( arm & x86).