* Add option parsing to `prompt_fresh_setup` to detect when options are
set during setup.
* Add `-a` option to enable almostontop behaviour, every time a command
is invoked the screen is cleared and the is prompt redrawn before the
command begins using the `preexec` hook. `-a` is disabled by default.
* Add `prompt_fresh_help` function to display a description of available
options using `prompt -h fresh`.
* Canonicalize all utility functions for the fresh prompt theme to
follow the `fresh_<name>` convention.
Fixes#1.
