Replace dashes with underscores in g:colors_name before calling function

Variable names in Vim script cannot contain dashes ('-').
Add 'base16-3024' colours

References #11.
Add 'base16-ashes' colours

References #11.
Add 'base16-atelierdune' colours

References #11.
Add 'base16-atelierforest' colours

References #11.
Add 'base16-atelierheath' colours

References #11.
Add 'base16-atelierlakeside' colours

References #11.
Add 'base16-atelierseaside' colours

References #11.