liboconfig/scanner.l: Added support for wrapping lines.

liboconfig/scanner.l: Added support for wrapping lines.

Lines may now be wrapped by using "\" as the last character before the
newline. This allows long lines to be split into multiple lines. This also
applies to quoted strings, which are, however, treated special in that
whitespace at the beginning of the following lines will be ignored. This
allows for nicely indenting the wrapped lines.

The following example:

  Foo a very very very long list of options \
      that does not fit on one line
  Bar "a very very very long string \
      which does not fit on one line"

... is equivalent to:

  Foo a very very very long list of options that does not fit on one line
  Bar "a very very very long string which does not fit on one line"

Signed-off-by: Sebastian Harl <sh@tokkee.org>
Signed-off-by: Florian Forster <octo@huhu.verplant.org>