Minor updates to the README.md

- Mainly smaller types, etc.
Add facility to write stimuli and expected responses to separate files.

- Two additional methods are now available, which allow to write the values of stimuli and expected response signals to two separate files.
Add signal caption functionality.

- Provide a signal caption in the testvector file every X-th testvector line (the value can be set by the user).
- Remove a small bug regarding the different number bases.