Changes decimal separator in a string numeric value to a point.
It is expected that value matches [+-]([0-9]*[decimal-separator])?[0-9]+
where decimal-separator can be any char except [0-9], + and -.

Returns numeric string with point as decimal separator,
which matches [+-]([0-9]*[.])?[0-9]+

## Usage

   (require '[utilities.string-formatter :refer :all])

   (to-numeric "123,567")
   => "123.567"

   (to-numeric "-5,89")
   => "5.89"

   (to-numeric "1")
   => "1"

   (to-numeric ",02")
   => ".02"

   (to-numeric "+8,2")
   => "+8.2"

   (to-numeric "-1")
   => "-1"

   (to-numeric "5,")
   => "5."

   (to-numeric "4;5")
   => "4.5"