Add a graphics option for nearest-neighbor and linear interpolation

[jakwings]

Ping #357. Currently there are "nearest-neighbor" (use British English "neighbour"?) and "linear".

But the "nearest-neighbor" is too long for in-game menu, so it goes to the next line. Suggestion?

p.s. It seems the code for DOSBox is not maintained anymore, should we remove all related code?

[jakwings]

Alternatives: nearest&linear pixelated&smooth

[ryfactor]

Nearest and linear sound most accurate, but pixelated and smooth are more descriptive. Maybe opt for the latter. I'm tempted to call linear or smooth, "fuzzy".

EDIT: This works on windows too by the way, just ignore Travis, it can't seem to locate some package on the cross-compiler.

[jakwings]

I prefer pixelated&sm👀th too. Rebased and check passed!