Improvements to beast::unit_test framework:
* Some runner member functions are now thread-safe.
* De-inline and tidy up declarations and definitions.
* arg() interface allows command lines to be passed to suites.
Update unit testing command line parser parameters:
A string passed by the '--unittest-arg' command line parameter is passed to
suites when unit tests run and can be used to customize test behavior.
* Add '--unittest-arg' command line argument
* Remove obsolete '--unittest-format' command line argument
Add 'sample' npm test:
test/sample-test.js is the smallest possible npm test.
Finalize autobridging implementation (RIPD-486, RIPD-491, RIPD-659):
* Taker refactor
* Add unit test support
* Perform flavor-aware crossings with flow quantization
* Implement 'issue/redeem' model for IOU transfers
[WIP] fixes
[FOLD] Rebalance XRP legs post-flow
[FOLD] Clarify some sig-checking code
[FOLD] Clarify code-flow in OfferCreate and misc. cleanups
[FOLD] Bridging over offers with same owner (RIPD-441)
[FOLD] typo
[FOLD] Groom order books during offer crossing