Add TokenizedVaultDepositor

[wphan]

PR continued in #55

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This PR introduces a new TokenizedVaultDepositor that may be initialized by a Vault's manager. Each Vault may have at most 1 TokenizedVaultDepositor, which cannot be closed after creation.

Token mint/burn amounts are calculated using IF math, with the convention: if_shares -> tokens and if_amount -> vault_shares. Management fee and profit share calculations on TokenizedVaultDepositor are identical to VaultDepositor.

New instructions:

• initialize_tokenized_vault_depositor
  • can be called once by manager to create a new TokenizedVaultDepositor
  • creates a new spl_token::Mint whose mint_authority and update_authority is the Vault
  • creates a metaplex::Metadata account
• tokenize_shares
  • deducts shares from the sending VaultDepositor and adds to the TokenizedVaultDepositor
  • mints tokens to the ATA owned by VaultDepositor.authority
  • check: vault_depositor.shares + tokenized_vault_depositor.shares is unchanged
  • check: tokens minted = change in supply
• redeem_tokens
  • transfer tokens to burn from user owned ATA to vault owned ATA and burns it
  • deducts shares from TokenizedVaultDepositor and adds to VaultDepositor
  • checks: vault_depositor.shares + tokenized_vault_depositor.shares is unchanged
  • check: tokens minted = change in supply