* Abstract constructing extrinsic and signing. * Initial impl of signer. * Implement get payload. * Clean up the code. * Improve docs. * Bump version. * Update core/sr-primitives/src/generic/unchecked_extrinsic.rs Co-Authored-By: Bastian Köcher <bkchr@users.noreply.github.com> * Fix tests & address grumbles. * Fix build. * Fix runtime tests. * Fix bound test. * Fix bound test.