Fix LineSeries() drawing hairlines when scaled

[fatcerberus]

LineSeries() is currently implemented as a line strip:
https://github.com/fatcerberus/minisphere/blob/v4.5.11/src/minisphere/vanilla.c#L2127-L2131

This method works well at 1x scale, but when the game window is zoomed, as sometimes happens with lower-resolution games or in fullscreen, the line segments become hairlines (thinner than a pixel) because the GPU only scales the vertices and not the line segments themselves.

Find a way to fix the implementation so that the lines have 1-pixel thickness, as those produced by Line(), preferably without producing visible "elbows" on translucent line strips.

[fatcerberus]

PointSeries() is also affected by this, since it uses ALLEGRO_PRIM_POINT_LIST. Just like with lines, points get scaled merely by scaling the point's coordinates; the GPU will never light more than a single screen pixel for a given point, even with a scaling matrix in play.

Note that this bug doesn't affect Surface#lineSeries() or Surface#pointSeries() because scaling never comes into play.

[fatcerberus]

This bug is fixed after changing to a new scaling algorithm (see 59b2556). The backbuffer is sized to the game resolution and scaled up on flip, so LineSeries() and PointSeries() now come out as they would in Sphere 1.x, regardless of the scale factor.