Fix time-domain calculations of the optimal observation filter

The calculations for the time-domain optimal observation filters have been fixed.

There are some minor improvements in other fields such as:

• A bug in obsFiltTD() that screwed up the dimensions of the arrays when there was only one source.
• A bug in ptSrcFieldTD() that screwed up the dimensions of the arrays when there was only one source.
• The virtual microphone geometry generation function was heavily modified, and its interface has changed.

This merge closes the Closes #8 (closed).

Virtual Sensing/README.md

@@ -11,6 +11,7 @@ The current structure of the section is shown below
 - Remote Microphone Technique
   - Observation filter calculation
     - Frequency domain (tonal)
+    - Time domain (broadband and causal)
 
 
 ## Dependencies
@@ -51,4 +52,5 @@ None.
 
 ## References
 
-[1] A. Roure, A. Albarrazin, *"The remote microphone technique for active noise control"*,  Inter-Noise and Noise-Con Congress and Conference Proceedings, Active99, Fort Lauderdale FL, pp. 1233-1244(12).
+[1] A. Roure, A. Albarrazin, *"The remote microphone technique for active noise control"*, Inter-Noise and Noise-Con Congress and Conference Proceedings, Active99, Fort Lauderdale FL, pp. 1233-1244(12).
+[2] S. J. Elliott, J. Cheer, *"Modeling local active sound control with remote sensors in spatially random pressure fields", Journal of the Acoustical Society of America, 137, pp. 1936-1946, (2015).