The variable name was misleading and hence renamed

This renames the input sftfilepath to sftfilepattern and adds
documentation on how that should be used, i.e. a colon separated list of
wildstring or exact matches. In globbing for all matches, the colon
split is added in. sftfilepath is still used by `Writer` since
an exact path is known.

Rather than starting with the fully-coherent Vsize, this now starts with
the input Nseg0 (i.e. from the SC search). and works back to Nseg=1.
The user is then left to check the V0 value and whether the search is
appropriate or not. Applies the idea to the follow-up example.

- Applies method to weak_signal method
- Adds methods to read/write setup files - this saves recalculating
  expensive optimial setups
- Simplifies notation and laoyout for generating setup and writing
  tables