Truncate the end of long token titles

By changing the autoresize rules on the token label, we can force the
label to appropriately size itself to the token title. Before, a
token’s label was sized to its content, meaning that if it was actually
longer than a line in the token field, it freely overflowed and was
clipped by the outer VENToken’s view. I also exposed the line break
mode for VENTokens as a whole, allowing a client application to change
the line break mode to one appropriate to their data (breaking in the
middle or beginning of the line, for example). Including this in a release
requires a minor version as it adds new API.
Personal preference, but can we make this
```objc
@property (assign, nonatomic) NSLineBreakMode lineBreakMode;
```
instead of a static variable?