Add ability to limit the number of decimal places

Signed-off-by: Richard Tomlinson <richard.tomlinson@matchesfashion.com>
Updated tests for precision

Signed-off-by: Richard Tomlinson <richard.tomlinson@matchesfashion.com>
Update README.md

Signed-off-by: Richard Tomlinson <richard.tomlinson@matchesfashion.com>