Trailing & Baseline Offset Unit String

[im-jersh]

I've added properties to allow placing the unit string to the left or the right (default) of the value string. In using this library in my own project that heavily uses currencies, I found that the default position of the unit string to the right of the value was not appropriate for currencies that have leading unit characters. The unitTrailing property will place the unit string to the right (by default or if this value is YES/true) or to the left (NO/false).

Also, in looking through the open issues for this library, I noticed somebody had requested adjusting the unit string's baseline offset. The unitBaselineOffset property value will offset the unit string's baseline by the input value.

Both new properties are IBInspectable.

It should be noted that extreme unitBaselineOffset values (either positive or negative) can force the baseline offset of the value portion of the string in the opposite direction.