Doc: Add currency formatting

- Add `.currencyFormatter( currency [, options] )`;
- Add `.formatCurrency( value, currency [, options] )`;

Fixes #238
Closes #351
Various: Visually split explicit and implicit dependencies

Add a linebreak to visually separate explicit and implicit
dependencies.
Doc: Change plural example

Amends "Plural: Create generator method".
Amends 3e1626e386e13269bac86d503d6dd3c3e9656f25
Ref #335
Ref #336
Util: Object extend

Ref #351