Errorcheck MoveFromCoord in case of short string

In pure algebraic coordinate notation there  must be a minimum of 4
characters. So we can return an error if this is not a given.
Later we even get problem in case the user just inputted one letter
because we use [2:] and [:2] to the string.
Merge pull request #3 from jubalh/error_check

Errorcheck MoveFromCoord in case of short string