Add .prefix() expression to {name}

[DenisCarriere]

Implemented in EOSIO CDT:

• https://github.com/EOSIO/eosio.cdt/issues/648
• https://github.com/EOSIO/eosio.cdt/pull/805/files

Example 1

name account = name{"my.account"};
name suffix = account.suffix(); // => "account"
name prefix = account.prefix(); // => "my"

Example 2

For names with multiple prefixes, split name at the first . dot to the right.

name account = name{"a.my.account"};
name suffix = account.suffix(); // => "account"
name prefix = account.prefix(); // => "a.my"

name subsuffix = prefix.suffix(); // => "my"
name subprefix = prefix.prefix(); // => "a"

[jafri]

Closed by 9597b8739bc388a63b03d083d928d528301be96b