Allow building plain armeabi binaries for android

Building with "make OS=android APP_ABI=armeabi" will
produce arm binaries that will conform to the armeabi
ABI - not using any features outside of armv5te by
default (but still optionally using the NEON functions at
runtime if detected - even though such devices should rather
use the default armeabi-v7a build).
Make the processing lib use mutexes from WelsThreadLib from the common library

This requires always building the WelsMutex* functions,
even if MT_ENABLED isn't set.
modify and correct SVC slice header parse
Include time.h in the MemoryAlloc test

This is required to get the time() function. This fixes building
on older MSVC versions.
Merge pull request #469 from huili2/svc_sh_bug_fix

modify and correct SVC slice header parse
Merge pull request #468 from mstorsjo/include-time-h

Include time.h in the MemoryAlloc test
Merge pull request #410 from mstorsjo/android-armeabi

Allow building plain armeabi binaries for android
Merge pull request #456 from mstorsjo/use-common-threadlib

Make the processing lib use mutexes from WelsThreadLib from the common library
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
Merge branch 'master' of https://github.com/cisco/openh264 into add_me_test
Merge remote-tracking branch 'origin/add_me_test' into add_me_test
complete test case