* Add build configuration for Mac
This patch implements Mac build basically based on Linux platform
implementations and configurations.
The document to build it on Mac has been updated as well.
* Update wasm_application.h
* Update lib_export.h
Add comments for the functions.
Enable setting external memory space for wasm app, the feature is disabled by default;
Remove wasm_application_exectue_* APIs from wasm_export.h which makes confused.
* Implement memory profiler, optimize memory usage, modify code indent
* Implement memory.grow and limit heap space base offset to 1G; modify iwasm build type to Release and 64 bit by default