We intend on splitting the address types and logic out into a separate
crate. In preparation for doing so, and so that we can grab the name on
crates.io, add an empty crate `bitcoin-addresses`.
Tie it in to the CI infrastructure.
Some of our CI shell scripts are meant only to be sourced and not
run directly however they include an initial shebang line, implying that
they should be run.
Remove the shebang line from `crates.sh` and the various `test_vars.sh`
scripts. Add a `shellcheck` directive to inhibit the no-shebang warning.
Fix: #2764
Tobin C. Harding
Jose Storopoli