Some MSGIDs added to error calls

No error calls without MSGID left according to mlint
join: uses strategy of strjoin to concatenate

- First convert all numeric values to string
- Then create a cell array twice the size of the input
- First row is the input, second row contains the delimiter
  except at the last position
- Concatenating over the linear index of the cell array, will give
  a properly joined string

This removes the need for a growing string in a for loop.

This performs the same functionality as strjoin in MATLAB, but
as this function was only introduced in a fairly recent version
(R2012a/b, I guess), it cannot be used for backward-compatibility reasons.
Removed returns and empty lines at end of function

 Return as a last command is superfluous -> removed
 Some blank lines removed as well (especially at the end of functions)
Merge pull request #242 from egeerardyn/cleanup

Cleanup