Bump required ffi version to 1.2.x

gcc-explorer doesn't build using node.js v0.10.25 with ffi 1.0.7
or anything below 1.2.x.
Compress source for permalink

Use lz-string (http://pieroxy.net/blog/pages/lz-string/index.html) to
compress source code for permalink usage.
Fix onCompilerChange when there is no compilers

If compilersByExe is undefined trying to access compiler.supportedOpts
throws an exception. This happens when gcc-explorer can't find available
compilers.
Add /usr/bin/g++ to default properties file

/usr/bin/g++ is added as default only if compilers is not defined.
Utilize Android NDK installations

NDK comes with a handful of compilers and this patch modifies gcc-explorer to utilize them.

Standalone invocations of toolchains inside NDK requires --sysroot
option to be set to a correct 'system/platform' directory inside NDK
however this isn't necessary for trivial compilations.

Tested with NDK r9c.

[1]:
https://android.googlesource.com/platform/ndk.git/+/master/docs/text/STANDALONE-TOOLCHAIN.text
Merge pull request #45 from auselen/master

Some changes to get gcc-explorer working for me