Added a getFriendlyString method

I added this function for an upcoming project, and thought that it should be reviewed for consideration to be included in the base source.

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Added the ability to get a friendly string representation of a numeric,
which will respect the sign if specified.

ie:
1000 -> 1.0K
100,000 -> 100.0K
1,000,000 -> $1.0 million
1,000,000,000 -> $1.0 billion
1,000,000,000,000 -> $1.0 trillion