This introduces a new parameter, 'key_val_separator', which
can be set in order to override the string that is used
as a separator between the key/value pair of a setting line.
The default is ' = ', but you could set the param to '=' if
you don't want to include whitespace in your settings file.
This commit does the following:
* Fixes a bug in ExternalIterator
* Adds support for a "global" section before the first named
section at the beginning of the INI file
* Improves test coverage
characters. Fixed writing to file without any sections at all.
Fixed exists checking for variable type by always casting to string
and added all the tests for the above items.
