Format quotation marks and newlines for PO export

[felixvd]

Fixes https://github.com/leonelquinteros/gotext/issues/60.

As described in the issue, this:

    po := gotext.NewPo()
    strings := map[string]string{"myid": "test string\nwith \"newline\""}
    for k, v := range strings {
        po.Set(k, v)
    }
    po_bytes, _ := po.MarshalText()
    fmt.Println(string(po_bytes))

currently outputs this:

msgid ""
msgstr ""

msgid "myid"
msgstr "test string
with "newline""

This breaks format and causes xgettext to throw errors if the file is used. After this PR, the output is:

[...]
msgid "myid"
msgstr "test string"
"with \"newline\""

My apologies for not adding tests. Please feel free to edit/push to this branch.

[leonelquinteros]

Hi @felixvd , thanks for your contribution!

It looks like this PR is breaking the build process (didn't reached the tests). Could you review that to ensure at least old tests are passing?

Also, adding tests for this use cases would be welcome, otherwise we'll wait until there are tests in place to cover for them before merging the PR.

[felixvd]

My bad, I edited quickly in the Github web interface.

Fixed and added a test.

[leonelquinteros]

@felixvd Please check the test error now.

[leonelquinteros]

Thanks for your contribution @felixvd !!