add safety check for bit-reading for headers
refine android build, add TARGET option to specify target in sdk
init the spatial last spatial picture if excption
update README
Merge pull request #323 from huili2/check_bit_read

add safety check for bit-reading for headers
add missed namespace for encoder, remove un-used file
Merge pull request #321 from licaiguo/add-android-target-option

Add android target option
Merge pull request #324 from volvet/add-missed-namespace-for-encoder

add missed namespace for encoder, remove un-used file
Squashed merge from writenal_refactor2
fix the crash issues by changing the type iMbWidth & iMbHeight.
Merge pull request #326 from licaiguo/fix-allocate-large-memory

fix the crash issues by changing the type of iMbWidth & iMbHeight.
Ignore project.properties

This file is autogenerated when building nowadays.
Merge pull request #327 from mstorsjo/ignore-android-files

Ignore project.properties
Enable x86 assembly by default if building for x86 android

Most users would probably miss enabling it otherwise.

It can still be disabled manually by passing USE_ASM=No on the
make command line.
Chain build commands using && instead of ;

This makes sure the build aborts as soon as possible if there is an
error, instead of having the error message drown in all the
following output.
Don't quote the android building commands in sh -c ''

The full command line can be written as such without any extra
wrapping.
Don't use LOCAL_PATH in LOCAL_SRC_FILES

These files are automatically relative to the directory of the
current makefile.
Run ndk-build from the android project top level directory

One doesn't need to run the ndk-build command from within the
jni subdirectory, calling it from the project top level directory
works just as well.

Also remove an unnecessary step of cd ../../../.. at the end -
since all make commands are run in a subshell, we don't need to
restore the current working directory afterwards.
Pass the right -mfpu flags for the armeabi-v7a target without NEON
Fix building the gtest library when targeting android

The main purpose is to make sure that the build doesn't fail
if the build directory contains the gtest subdirectory, although
the unittests also could be run on a device.