Feature/openssl seal

Updated to use openssl_seal

• Migrated to use openssl_seal with array of public keys for encryption
• added config to allow selection of cipher

• removed database requirement & migrations

• updated tests & documentation
• added facade alias to package

• Note: Major update so should be tagged as 2.0.0

• Note: Test in conjunction with the eloquent-model-encrypt (not required)

• Setup: php artisan asynckey