Adds error message to bigg::loadMemory in case of error when opening file #30

[dejaime]

Adds an error message mentioned in issue https://github.com/Josh4428/bigg/issues/30 Added messages appear as follows:

build $ examples/cubes/cubes
ERROR: Failed opening file shaders/glsl/vs_cubes.bin
Failed loading shader shaders/glsl/vs_cubes.bin
“examples/cubes/cubes” terminated by signal SIGSEGV (Address boundary error)

This change however does not prevent the program from crashing, but improves usability when compared to previous output:

build $ examples/cubes/cubes
Segmentation fault (core dumped)

Thank you very much!