Add domain based download

documentation/data-sourcing

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+The obvious question for anyone starting with this product is:
+where do I get the data from?
+
+The basic idea of BCMRs have 3 main sources of data;
+
+1. DNS. Basically a domain name and we expect a certain file there.
+2. on-chain. Using the concept of authority-chain and comments in
+   transactions that point to URLs on the net.
+3. Payment requests from wallets and point of sale systems.
+
+
+What is important to understand that the bcmr is decentralized. We are
+not trying to create one source of truth for the whole world, we would
+fail spectacularly as the system grows. So the goal is more humble and
+the approach is matched to that.
+
+The bcmr concept gives people the ownership over their own data, which
+is the basis of that decentralization mentioned. Companies can store it
+on their own website. Companies can include it in payment requests whenever
+users visit their store. And totally anonymous users can store data on
+the cloud and refer to it on-chain.
+
+What the BCMR registry project adds is the ability to add a quick lookup
+of data for wallets and users.
+And at the same time this project adds trust indications to the data. It
+is mostly up to the operator to specify that trust, though.
+
+Trust is important since if people start to depend on this system, it's
+decentralized nature will mean the general public can't distinguish between
+a scam or the real thing.
+Wallets that ignore trust will start showing product advertisements to
+end users simply because the advertiser sent a payment to a wallet worth
+a fraction of a cent.
+
+Trust is most of the time local, someone in America won't be able to decide
+which metadata file is real when it is about some Chinese or Indian company.
+
+The conclusion is that the best way to operate a registry is to have the
+operator insert trust into the system. Even if only by marking spam as such.
+
+# DNS starting point.
+
+The DNS starting point is obvious for most bigger projects and companies.
+You create a text file (of any name) in the in/trust/ directory. In it
+you put at least 2 lines;
+  domain=flowee.org
+  trust=ultimate
+We will then check and download the metadata. Refreshing it about once a week.
+
+# on-chain.
+
+The registry does not have any direct connection to the blockchain, but
+transactions with bcmr metadata are accepted.
+Simply place the transaction raw file in the bcmrs/ directory and we will
+download and verify the referenced metadata file.
+
+Notice that this will by default have no relevant trust level (none).
+When the transaction belongs to a chain of transactions on an auth-base does
+the trust level go up.
+See the 'trust' docs on how to provide a specific trust assessment.
+
+Anyone wanting to use the BCMR as a simple "all bcmrs known" simply needs
+to find all relevant transactions on the chain with the right comment and
+drop them in the bcmrs/ dir to make that happen.
+
+# Auth-chain (from wallets of payment requests).
+
+The owner of an auth-base is expected to have the entire chain of
+transactions that they could share with us. Importing this will make
+all metadata files that use the auth-base as their identity be checked
+to actually be referred to from that auth-chain. And they will then
+automatically inherit the trust of the auth-chain. The token categories
+inherit this trust level as well.
+
+An auth-chain file (format to be determined) needs to be dropped in the
+authchains/ subdir,