Improve b: variable names
Change API: consolidate NifflerNew/VCS commands into one Niffler cmd

- Remove ability to pass `find` args to the Niffler command.  I think
  this was an unnecessary feature, you can always type to filter down
  the list more, rather than using find to do things Niffler wasn't
  intended to do.
- Change also serves to simplify the API and make Niffler easier to
  expand or add more commands as needed
Modify grep filter to limit number of matches reported

- Should speed up total search time by cutting down on time spent
  redrawing lines after filtering all candidates
Remove 'shelltemp' logic. Unnecessary with switch to system call
Move prompt to bottom; replace autocmds with getchar/echon loop.

- Move prompt from top of the screen to the bottom utilizing a
  while/getchar/echon loop.  This change was motivated by the desire to
  replace the buggy prompt line I was attempting to emulate previously.