Sperm whale IPI computation

This is a module for Sperm whale Inter-pulse interval (IPI) computation, designed to work with the Pamguard Beta release only. It uses cepstral analysis to compute the Inter-pulse interval of sperm whale clicks.Two related signal processing methods are used to obtain an IPI:

Method 1 computes the IPI for each click and then averages these IPIs together as described by Gordon (1991) - J. Zool. Lond. Vol 224 pp 301-314

Method 2 computes the ensemble averaged cepstrum from all clicks and then picks one IPI from this ensemble averaged signal similar to Teloni (2007) - J. Cetacean Res. Manage. Vol 9(2), pp 127-136.

This 2018 update is the first real update to the PAMGuard IPI plugin in nearly 10 years. The 2018 update includes newly written documentation, and it streamlines configuration of the plugin by combining the two required modules (formerly EchoDetector & IpiDemo) into a single plugin. This update also simplifies the settings, and adds proper support for saving data to the Pamguard database and binary files. The 2018 updated plugin has been tested on PAMGuard 2.0.12c.