update bespoke
update gems
add taper parameter

also move overshoot and taper to
new category 'optical corrections'
appert, corner, overshoot, taper -> optical corrections
move spec to proper location
remove obsolete comment (amend 6fb489b9)
remove unnecessary method (we have attr_accessor)
move metaflop instance creation to class
refactor configuration to specific methods
generation of fonts into its own class
use metaflop_create in all app.rb
update font param spec (-> preview flag)
extract file logic from font_parameters to own class
make instance_param more readable (less spaghetti)
remove unnecessary nil check
add pry for development
simplify to_hash method
fix default argument
use declared fonts from config yml
extract modular parameters to own class