Adjust account meta data to allow specifying separately per account

[Nef10]

Currently the keys are applied to all account types. This change
refactors the meta data handling, so that for every type the
Wealthsimple accounts can be set separately.
It also now only requires one entry if an account is only used for one
type.

To see how to apply meta data now, see the readme.

Fixes #41

[github-actions]

Coverage after merging metadata into main

34.95%

Coverage Report

File	Stmts	Funcs	Lines	Uncovered Lines
Sources/SwiftBeanCountWealthsimpleMapper
LedgerLookup.swift	84.80%	90.91%	83.50%	66–72, 74–83
WealthsimpleConversionError.swift	100%	100%	100%
WealthsimpleLedgerMapper.swift	0%	0%	0%	100–112, 126–161, 170–182, 185–216, 218–225, 227–232, 234–249, 25, 251–257, 259, 26, 260–269, 27, 270–271, 273–279, 28, 281–288, 29, 291–299, 30, 301–307, 309, 31, 310–313, 34–37, 40–44, 47–51, 58, 62–64, 78–99
WealthsimpleTransactionRepresentable.swift	100%	100%	100%
Sources/SwiftBeanCountWealthsimpleMapper/Extensions
Amount+init.swift	100%	100%	100%
String+KebabCase.swift	100%	100%	100%