MAINT: better error message in construct_alphabets (#147)
MAINT: better error message in construct_alphabets (#147)

* MAINT: better error message in construct_alphabets

* MAINT: point to potential solutions

dit/dit,Autoplectic/dit,dit/dit,dit/dit,Autoplectic/dit,Autoplectic/dit,dit/dit,dit/dit,Autoplectic/dit,Autoplectic/dit