Half-star ratings are rounded up to the next int

[bohning]

Song ratings are averaged to the nearest half star

but the Syncer rounds that up to the next integer.
The reason this happens is because we are counting the number of occurrences of star.png in the rating string, but this also matches half_star.png. Thus, this requires ratings to be either a float (currently an int), or use half stars as the base measure and then go from 0 to 10. There is a Unicode code point for LEFT HALF BLACK STAR (U+2BE8) that can be used.