reading twice a config file that changed would not overwrite old in-memory config

[fabricemarie]

Fix a bug where reading twice a config file that changed would not overwrite the old in-memory config.
The previous version would simply append the new version (with the same section name) in the section array and it would be ignored.

[robik]

Thanks for pull request, however I think that we should not break the API compatibility for any bugfix. I am willing to merge this if it is backwards compatible (speaking of making section children a hashmap).

[fabricemarie]

The sections and subsections work the same way as they used to from outside.

The only incompatible change is:

-    public IniSection[] sections() @property
+    public IniSection[string] sections() @property