starting documenting xywh_shorthands

lib/squib/args/unit_conversion.rb

@@ -17,7 +17,7 @@ module Squib
         when /deg$/ # ends with "deg"
           arg.rstrip[0..-3].to_f * (Math::PI / 180.0)
         when /c(ell)?[s]?$/ # ends with 'c', 'cell', or 'cells'
-          arg.rstrip[0..-2].to_f * cell_px
+          arg.sub(/c(ell)?[s]?$/, '').to_f * cell_px
         else
           arg
         end

lib/squib/args/xywh_shorthands.rb

@@ -7,7 +7,6 @@ module Squib
       HEIGHT_MINUS_REGEX = /^height\s*\-\s*/
       WIDTH_DIV_REGEX = /^width\s*\/\s*/
       HEIGHT_DIV_REGEX = /^height\s*\/\s*/
-      CELL_REGEX = /^c[ell]?[s]?\s*/
       MIDDLE_PLUS_REGEX = /^middle\s*\+\s*/
       MIDDLE_MINUS_REGEX = /^middle\s*\-\s*/
 
@@ -32,10 +31,12 @@ module Squib
           n = UnitConversion.parse(n)
           deck.height - n
         when WIDTH_DIV_REGEX # e.g. width / 3
-          n = (arg_s.sub WIDTH_DIV_REGEX, '').to_f
+          n = arg_s.sub WIDTH_DIV_REGEX, ''
+          n = UnitConversion.parse(n).to_f
           deck.width / n
         when HEIGHT_DIV_REGEX # e.g. height / 3
-          n = (arg_s.sub HEIGHT_DIV_REGEX, '').to_f
+          n = arg_s.sub HEIGHT_DIV_REGEX, ''
+          n = UnitConversion.parse(n).to_f
           deck.height / n
         when MIDDLE_PLUS_REGEX # e.g. middle + 1.5in
           n = arg_s.sub MIDDLE_PLUS_REGEX, ''