Also propagate the comments

[tetrode]

Adding the possibility to also propagate the comments when writing the ini file. Works as follows:

$ini = 'piwik.ini';
$reader = new \Piwik\Ini\IniReader();
$config = $reader->readFile($ini);
$comments = $reader->readComments($ini);
$writer = new \Piwik\Ini\IniWriter();
$writer->writeToFile('piwik-new.ini', $config, '', $comments);

Things that do not work:

1 pre-section comments disappear:
; section comment
[MySection]
; option comment
myOption = 1

becomes
[MySection]
; option comment
myOption = 1

2 Individual array comments disappear:
[MySection]
; comment a
ar[] = "a"
; comment b
ar[] = "b"
; comment c
ar[] = "c"

becomes
[MySection]
; comment a
ar[] = "a"
ar[] = "b"
ar[] = "c"

[coveralls]

Coverage decreased (-11.7%) to 70.673% when pulling a37cd9f on tetrode:patch-1 into bd2711b on piwik:master.

[mattab]

Thanks for the PR @tetrode

Could you please add some unit/integration tests, to make sure your feature will not break in the future?