This commit converts value to a property so that it
can be managed and modified when a file already has
a value set.
It was previously treating the line creation state
the same as the update case, which is not in
alignment with Puppet's model.
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.
