* config parser now handles quoted values correctly. This doesn't hamper
  multi-line support.
* added regression test to travis to assure we will be warned if we
  rewrite and break the user's .gitconfig file
* only rewrite configuration files if we actually called a mutating
  method on the writer. Previously it would always rewrite it.

Fixes #285

Previously, the implementation would gladly reset new commits in submodules,
and/or reset a dirty working tree.

Now the new force_reset/force flag has to be specified explicitly to get back
to the old behaviour.

All submodule tests except for one are working.

Assured unicode values are supported when reading the configuration,
and when getting author/committer information from the environment.

Fixes #237

A test verifies it's truly working.

Related to #238

We implement it as described in this article:
http://stackoverflow.com/questions/1557183/is-it-possible-to-include-a-file-in-your-gitconfig

Thus we handle

* cycles
* relative and absolute include paths
* write-backs in case of writable GitConfigParser instances

Fixes #201

This brings us much closer to what git can do, and should at least prevent errors while reading
configuration files (which would break a lot of features, like handling of remotes since these rely
reading configuration files).

Fixes #112