[v27] Update build for iOS with x86_64 version for 64 bit simulator
[v27] Add arm64 architecture in double-conversion
[v27] Fix a problem in autoconf that ios_arch for simulator is forced to i386
[v27] Update configure
Merge pull request #27 from pandamicro/27_64bit

[v27] Support arm64 and x86_64 architecture for iOS 64 bit device and simulator