Converts a String to an std::pair of int64_t (long long), which contain the size or 0 if none could be parsed. Any delimiter except digits(0-9), a minus sign(-) or a plus sign(+) between width and height are allowed. If a plus or minus sign is used as a delimiter, it must immediately be followed by the second size number. This allows for formats such as: 100x100, 100:100, 100p100, 100@100, 100+100 and so on, but not formats such as 100+:100, 100ThisIsSomeReall+yLongText100, etc.
The parameter 'allowSquare' also determines what to do when the height parameter is not found. A value of true will have the function return <width,width> instead of <width,0>.
A bug in Visual C++ 2013 32-bit & 2015 32-bit causes the C++ compiler to incorrectly align the vec3 and vec4 structs to 8-byte instead of 16-byte, resulting in a crash if the target PC supports SSE. Visual Studio 2017 and 64-bit builds are not affected.
Related: #9
