Minor changes and additions

+ Added parameter to control whether mathematical commands are added or
not - they're many and may not always be necessary or even useful;
+ Added optional command name prefix and forced category to the utility
methods for finding/registering commands;
> Changed constructor of the MethodCommandData attribute to take no
parameters and made the setter of its properties public, allowing the
usage of named parameters on construction - all default command
definitions were changed to use the new declarations.