Multiple ways to allow duplicate Vouchers to spawn

[borb43]

Fixes allow_duplicates = true in in_pool and SMODS.create_card so that it works for allowing duplicate vouchers

Additionally adds a new SMODS.voucherman(voucher_key) function, which acts similarly to SMODS.showman but works for only vouchers. This is made a seperate function as to not change behaviour of existing SMODS.showman hooks.

Additional Info:

• I didn't modify api's or I've made a PR to the wiki repo.
• I didn't modify api's or I've updated lsp definitions.
• I didn't make new lovely files or all new lovely files have appropriate priority.