We use crate renaming to remove grin prefix, as result imports for util and keychain crates start with crate::
which looks like a part of the current crate. This PR fixes it.
Also some small improvements were made.
If this approach works I'll replicate it to other crates.
* tx combinators now take operate on Result to allow for more robust errors handling
replace with_fee() and with_lock_height() with a more flexible with_features()
* pass kernel features in as arg to build::transaction()
* fix chain tests
* fix pool tests
* do not pass kernel around in the combinators
just set it once on the tx when building
* build::partial_transaction now takes a existing tx to build on
Quentin Le Sceller