Bug fixes and new APIs

[donmccoy]

Problems addressed by these changes:

• Output of ZeroFFT function is scaled down by a factor of two.
• Results of ZeroFFT function are the real portion of the complex value, rather than the magnitude
• Application of the hanning window was manditory (feature request to make it optional).

Scope:

• Added two new API's that complement the existing function (which was not changed).
• New functions make hanning window optional.
• Fixed a bug in the core FFT function that was scaling results down by a factor of two (users of the old API will see this as a doubling of the magnitude of the results).

Known limitations:

• none

Testing:

• Added new tests\ directory
• Included a test for each of the new API functions (confirmed results match matlab/python).