Bitcoin Testnet backends were removed.
This broke our tests that work purely on local data but nevertheless
need to know backend URLs. Because the design is less than ideal.
Here, we do a little cleanup:
* blockbook URLs are respected
* Dogecoin is now supported by our blockbook backend so we don't need
a special tx-api implementation
* it's possible to instantiate a TxApi that is backed by the cache,
without a known URL
* relevant tests now make use of this feature
This clarifies the intent: the project is licenced under terms
of LGPL version 3 only, but the standard headers cover only "3 or later",
so we had to rewrite them.
In the same step, we removed author information from individual files
in favor of "SatoshiLabs and contributors", and include an AUTHORS
file that lists the contributors.
Apologies to those whose names are missing; please contact us if you wish
to add your info to the AUTHORS file.