* Add and use subxt-signer crate for WASM compatible signing
* cargo fmt
* dev keypairs already references
* WIP fix various breakages
* re-jig features to be simpler and various test fixes etc
* doc and web fix
* fix various bits and pieces
* fix a test I broke
* dev-deps can't be linked to in docs, hrmph
* cargo fmt
* another doc link
* document the subxt_signer crate more thoroughly
* move feature flag for consistency
* more docs, no default subxt feature flag on signer, update release instrs
* Add missing license header
* unwrap_inner => into_inner
* extend a test a little to better check derive junctions
* note more clearly that the crypto bits come from sp_core::crypto
James Wilson