Enforce various configuration options

[peer2f00l]

Currently many different configuration options exist but are unimplemented.

Ordered by priority, high to low.

• maximum_borrow_asset_usage_ratio maximum_borrow_asset_usage_ratio #12
• maximum_borrow_duration_ms maximum_borrow_duration_ms #17
• minimum_borrow_amount Borrow Limits #18
• maximum_borrow_amount Borrow Limits #18