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).

README.md

@@ -86,7 +86,7 @@ The project is licensed under the ***MIT License***, which is a rather unrestric
 
 
 ## Versioning ##
-The project uses [semantic versioning](https://semver.org/) and the current version is **v0.2.3**.
+The project uses [semantic versioning](https://semver.org/) and the current version is **v0.2.4**.
 
 
 #### **Important**