Support building on Mac OS X

Here is an initial effort to make the current code built and running on Mac OS X (possibly on Linux too). They are mostly trivial syntax changes, but we need to ensure it still work on Windows with any harm.

1. As you mentioned on email, we should check if `get_command_argument()` available on Intel Fortran compiler. It already looks like [standard-compliant](https://software.intel.com/sites/products/documentation/doclib/stdxe/2013/composerxe/compiler/fortran-mac/GUID-0ECA8F74-93D1-4005-8DE2-BF9DF2B78719.htm) though.

2. It seems Windows and Mac (as well as Linux?) have different naming convention for exported functions. Uppercase `CROP()` has been used on Windows, but what found out to be working on Mac was lowercase trailing `crop_()`.

There might be some other revealing cases as we go through porting. I'll try to spot any once working datasets available.