Type encoding for ledger account type.

This type covers both balance sheet and income statement account types:

1. For balance sheet accounts:
2. Asset (AccountKindAsset)
3. Liability (AccountKindLiability)
4. Equity (AccountKindEquity)
5. For income statement accounts:
6. Revenue (AccountKindRevenue)
7. Expense (AccountKindExpense)

FromJSON and ToJSON instances, too:

>>> Data.Aeson.decode @AccountKind "\"ASSET\""
Just AccountKindAsset
>>> Data.Aeson.decode @AccountKind "\"LIABILITY\""
Just AccountKindLiability
>>> Data.Aeson.decode @AccountKind "\"EQUITY\""
Just AccountKindEquity
>>> Data.Aeson.decode @AccountKind "\"REVENUE\""
Just AccountKindRevenue
>>> Data.Aeson.decode @AccountKind "\"EXPENSE\""
Just AccountKindExpense
>>> Data.Aeson.encode AccountKindAsset
"\"ASSET\""
>>> Data.Aeson.encode AccountKindLiability
"\"LIABILITY\""
>>> Data.Aeson.encode AccountKindEquity
"\"EQUITY\""
>>> Data.Aeson.encode AccountKindRevenue
"\"REVENUE\""
>>> Data.Aeson.encode AccountKindExpense
"\"EXPENSE\""

Provides textual representation of a given AccountKind.

>>> accountKindText AccountKindAsset
"Asset"
>>> accountKindText AccountKindLiability
"Liability"
>>> accountKindText AccountKindEquity
"Equity"
>>> accountKindText AccountKindRevenue
"Revenue"
>>> accountKindText AccountKindExpense
"Expense"

Type encoding for account values.

This definition provides both the AccountKind and an arbitrary object identifying the account. This arbitrary nature provides flexibility to use-site to use its own account identity and accompanying information when required.

>>> let acc = Account AccountKindAsset (1 ::Int)
>>> Data.Aeson.encode acc
"{\"kind\":\"ASSET\",\"object\":1}"
>>> Data.Aeson.decode @(Account Int) (Data.Aeson.encode acc)
Just (Account {accountKind = AccountKindAsset, accountObject = 1})
>>> Data.Aeson.decode (Data.Aeson.encode acc) == Just acc
True