Add documentation about how to build the different ABI variants for android
Merge pull request #470 from mstorsjo/android-abi-docs

Add documentation about how to build the different ABI variants for android
fix SM_FIXEDSLCNUM_SLICE bug, add SM_AUTO_SLICE mode
modify configure files
Remove a dubious/unnecessary workaround for an issue in a nonstandard toolchain

There's no requirement to work with the Intel NDK. The NDK build
files don't even need to create any cpufeatures subdirectory since
all of the cpufeatures library is handled within the normal build
system. Finally, the encoder makefile tried to create a directory
for "welsdecdemo", not anything for "welsencdemo".

Thus, if this really was necessary, it would already have been noticed
that it missed an entry for "welsencdemo". Therefore, remove this
hack/workaround.
Merge pull request #471 from ruil2/encoder_slice

fix SM_FIXEDSLCNUM_SLICE bug, add SM_AUTO_SLICE mode
Merge pull request #472 from mstorsjo/android-remove-mkdir-workaround

Remove a dubious/unnecessary workaround for an issue in a nonstandard toolchain
Remove something that looks like a personal todo note from the Android makefiles
Merge pull request #474 from mstorsjo/remove-todo-comment

Remove something that looks like a personal todo note from the Android makefiles
Merge remote-tracking branch 'upstream/master' into travis.osx