Merge pull request #301 from alex-ross/master

Updates thousands separator for SEK to correct value.
Add russian_central_bank to README
Merge pull request #302 from rmustafin/russian_central_bank_to_readme

Add russian_central_bank to README
Actually should only allow to multiply a money by a number
More readable by using if else
Update CHANGELOG and AUTHORS
Merge pull request #305 from viettienn/correct-money-multiply-operation

Actually should only allow to multiply a money by a number
Use coerce to allow reversed argument order when doing mathematical operations.
Updated AUTHORS and CHANGELOG
Remove un-necessary self
Never have to check the same currency as it is done in bank#exchange_with, remove some unnecessary self.
Merge pull request #307 from andriusch/master

Allow reversed order of arguments when doing mathematical operations
Merge pull request #308 from RubyMoney/refactor-arithmetic-module

Refactor arithmetic module
DRY out the creation of big decimals
Merge pull request #310 from orien/master

DRY out the creation of big decimals
Money#dollars & Money#amount return BigDecimal

Money#dollars and Money#amount methods return numbers of type BigDecimal
rather than Float. Floats have esoteric precision qualities that make
them a bad match for representing values of currency. The Money gem
should set an example and promote the use of BigDecimal.
Comments describe Money#amount returning BigDecimal
Post install message for #amount and #dollars

A warning for people upgrading to version 6 that the Money#amount and
Money#dollars methods now return BigDecimal values.
new option :sign_positive

  * adds a + sign to positive values
update list of authors and changelog