Add dependency on Radix

Radix is a very easy to use Ruby library for converting numbers to and from any
base.

https://github.com/rubyworks/radix
Serialize Integers and Floats as octal numbers
Change handling of Strings in parsing methods

This changes the parser to hold on to the "s around a string until
DSON::Value::StringValue.so_parse is called, where they are removed. This
makes it possible to distinguish true strings from numbers.
Parse Integers and Floats as octal numbers
Merge pull request #2 from petedmarsh/octal-numbers

Serialize/parse octal numbers