* First steps converting transaction workflow to be aggsig-enable
* integrating updated version of aggsig, which gives greater control over the contents of e
* added wallet transaction test to testing framework to enable testing the whole thing, completed interaction as far as inital response from recipient
* more aggsig work, final signature is produced now
* Construction of aggsig transaction now working to the point of the signature being built
* aggsig transactions working end-to-end in the nominal case
* refactor aggsig verify from commit and fix some tests
* more cleanup and test fixing
* cleaning up automated tests
* test+formatting fix
* allow selecting a commit while providing a key index
* added static reference to libsecp that can be called throughout
* don't serialise rangeproof to json if it's not desired
* added global slog instance, changed all logging macro formats to include logger instance
* adding configuration to logging, allowing for multiple log outputs
* updates to test, changes to build docs
* rustfmt
* moving logging functions into util crate
