Regression: set() no longer supports strings

[colinodell]

PR #100 (released in version 1.5.1) broke the ability to use string values in the set() method. This was likely due to the docblock suggesting that only float values could be used, even though the Python, C# and Java libraries all explicitly support strings, and string values previously worked with this library in 1.5.0 and earlier versions.

I'd be happy to submit a fix for this :)