Bug fixes and language files

• Follow Wordpress plugins directive
• Add language files and translations for English and Spanish
• Bug fixing

First release

First Release Custom Price by User Role v1.0.0

• Add capability to have custom price for each member in Woocommerce Store.
• Add admin panel page options to show/hide members' custom price.
• Add admin panel option to show custom prices as a discount of the regular price.
• Add capability to read and write custom prices through the Woocommerce API REST.