MNT: Only download fsl_course_data category by default

Default behaviour, when using the default manifest, is now to only present/download files in the fsl_course_data category. This behaviour is only active when using the default manifest, and can be overridden by specifying --category all (although at the moment, all files in the default manifest are in the fsl_course_data category anyway).

Also prefix downloaded files with their category to reduce the likelihood of collisions across different categories (e.g. registration.tar.gz from FSL course and from grad course). This does not prevent collisions in extracted paths though.

Behaviour of the --force option has also changed (primarily for testing purposes). It now causes all selected categories/modules to be downloaded (honouring the above rules).

CHANGELOG.md

 # `fsl_add_module` changelog
 
 
+## 0.4.0 (Tuesday 24th January 2023)
+
+ - Changed the default behaviour so that only files in the `fsl_course_data`
+   category are downloaded. This can be overridden by specifying `--category
+   all`.
+ - Prefix downloaded files with their category name to reduce the likelihood
+   of collisions across different categories (e.g. `registration.tar.gz` from
+   the FSL course and from grad course data sets). Nothing is done to prevent
+   collisions in extracted paths from different archives though.
+ - The `--force` option can now be used without specifying any modules - it
+   causes all modules in the default/selected cateogories to be downloaded.
+
+
 ## 0.3.2 (Wednesday 1st September 2021)
 
  - Changed the default manifest URL to