Handle escape sequences in unquoted strings

[filipnavara]

Issue src-d/go-git#681

I did git clone --bare E:\Git\emclient\emclient.git, which created the following config file:

[core]
	repositoryformatversion = 0
	filemode = false
	bare = true
	symlinks = false
	ignorecase = true
[remote "origin"]
	url = E:\\Git\\emclient\\emclient.git

Git parser accepts it just fine:
https://github.com/git/git/blob/27c929edd6cccfbbedf2fbb8a3175bc7e01bf6c7/config.c#L537-L560

[hairyhenderson]

I ran into this error running the tests for src-d/go-git - I guess gcfg needs a new release to get picked up by a go get -u

/cc @smola

[smola]

@hairyhenderson Thanks for the heads up, v1.4.0 is now tagged.