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).

CHANGELOG.md

+### v0.2.4 ###
+**Virtual Sensing**\
+\* Corrected time-domain observation filter calculations.\
+\* Removed scaling from the cross-correlation calculations in the time-domain optimal observation filters.\
+\* Fixed bug in time-domain observation filter that screwed up dimensions of the filters when only one source was present.
+
+**Sound Fields**\
+\* Fixed bug in time-domain point source signal calculations that screwed up dimensions of the resulting arrays when only one source was present.
+
+**Utilities - Geometries**\
+\* The virtual microphone geometry generation function has been heavily modified and its interface has changed in a **backward incompatible** way. It is now more generic and allows for "arbitrary" size of each Cartesian dimension of the geometries as well as different number of sensors along each dimension.
+
+
 ### v0.2.3 ###
 **Virtual Sensing**\
 \+ Added function to estimate the observation filters in the time-domain.\