Adds teos crate docs plus some smalls fixes

[sr-gi]

Watcher:

• Modifies LocatorCache to hold BlockHash instead of BlockHeader. The headers were not really used for anything aside from checking the hash chain.
• Refactors for loop to use iterators.

Carrier:

• Renames Receipt to DeliveryReceipt

Config:

• Makes Config::verify use bitcoin::network::constants::Network so code is cleaner and data is parsed from an enum instead of from Strings.

DBM:

• Updates DBM method visibility. Also store_key -> store_tower_key