tests: Add a test for load_file with wide Unicode name
Use _wfopen and fseeko64 on MinGW in C++11 mode

Since MinGW 4.5 does not define these functions if __STRICT_ANSI__ is defined
(in case of _wfopen it defines it inconsistently between stdio.h and wchar.h)
use the baseline functions for MinGW 4.5 and earlier.

Fixes #23.
docs: Update changelog to mention MinGW load_file fix
Update version number in README.md
Merge branch 'master' into compact