Fixes#1369.
Prior to this commit, the docs on fidelity bonds stated that expired
fidelity bond utxos (which are spendable), can be spent in coinjoins as
a Taker, but that is not correct - they can only be spent in a
non-coinjoin transaction (direct send).
Add a new helper module to calculate fidelity bonds values and stats, and a script to use it.
The goal is to give as much information as possible to the user before
committing to a fidelity bond.
Closes#1247.
This consists of an inclusion of the bond value exponent into the config
that the user can alter, and a change of that from 2 to default 1.3.
Also updates the fidelity bond documentation to account for those
changes, including the units used in ob-watcher, but not the calculation
of fidelity bond attack resistance (which remains a TODO).
At least two people have been burned by creating two transactions
sending bitcoins to two timelocked addresses, and then finding that
yield-generator announces only one of them.
This commit expands the section talking about how only one UTXO will
be used. It also edits the text to refer to yield-generator's fidelity
bonds only in the singular, as previously they were referred to in
the plural (i.e. "fidelity bonds"), which possibly added to user's
confusion.