Change `.find_contract()` -> `.find_contracts()` to allow multi-search
for so called "ambiguous" contracts (like for `Future`s) such that the
method now returns a `list` of tracts and populates the contract cache
with all specific tracts retrieved. Let it take in an (unvalidated)
contract that will be fqsn-style-tokenized such that it can be called
from `.search_symbols()` (though we're not quite yet XD).
More stuff,
- add `Client.parse_patt2fqsn()` which is an fqsn to token unpacker
built from the original logic in the old `.find_contract()`.
- handle fiat/forex pairs with the `'CASH'` sectype.
- add a flag to allow unqualified contracts to fail with a warning msg.
- populate the client's contract cache with all expiries of
an ambiguous derivative.
- allow `.con_deats()` to warn msg instead of raise on def-not-found.
- add commented `assert 0` which was triggering a debugger deadlock in
`tractor` which we still haven't been able to create a unit test for.
0ef5da0881