Added #define's for deprecated POSIX names

Without these #define's to the current ISO C++ conformant names VS2013 throws the error C4996. E.g.:

> error C4996: 'rmdir': The POSIX name for this item is deprecated. Instead, use the ISO C++ conformant name: _rmdir. See online help for details.

There is a recent commit (https://github.com/cesanta/mongoose/commit/a6598a12781c395c87f7ff44a9d0a675b92da62a) related with this issue, but I wonder why weren't the other functions included too.