update commodity to v0.4

fix incomplete Action implementation for BalanceAssertion

- fixed clippy warnings
- formatted code
- bumped version to v0.8.1

major refactor to properly support user defined actions (#10)

* major refactor to properly support user defined actions, updated to v0.8.0

Fix building for default features accidentally including some items o…

…nly needed for `serde-support`

update changelog for v0.7.0

Fix changelog for v0.6.1

close #4 and close #5

- update rust_decimal dependency
- use Into and AsRef for arguments to make allocation clearer

Renamed argument in sum_account_states() and improved docs

updated commodity library to 0.3, renamed some types which were chang…

…ed for that version

AccountingError::Currency renamed to AccountingError::Commodity

improved serde support

 - removed Rc<Account> and replaced with AccountID
 - change AccountID to use an ArrayString to allow quick copy, and it was fixed size anyway
 - updated readme and examples