Include comments in `PO.Item` output

Fixes #5
Handle extracted comments
Document extractedComments
Merge pull request #6 from gabegorelick/serialize-comments

Include comments in `PO.Item` output
Release v0.2.5
Update contributors.
Fix build.
add reverse method of extract(string)

during PO.parse, an extract(string) method is called on each string to
unescape some characters (like " and \). This process should be reverted
in the toString method.

The PO spec says, that all strings should be C-Strings. Otherwise tools
like msgmerge (from the gettext package) will fail parsing po files written
by this library.
add some real world examples for c-strings in po files

make sure, if a file containing c-string messages is identical after being
parsed and written afterwards.
Merge pull request #7 from Open-Xchange-Frontend/write_escaped

add reverse method of extract(string)
Recompile for #7.
Release v0.2.6
Add support for obsolete items to fix broken parsing.
Remove unneeded if-clauses.
Release v0.2.7
add support for multiline string in headers

Some languages (such as Polish, Russian or Romanian) do have more
complicated plural forms. Those are still expressible by a more
complicated mathematical expression. However, the msgmerge tool of
gettext will in these cases write multiline header fields. When parsing
such files with this lib, the headers get screwed up, so this patch
provides an example (from a pl_PL po file) and fixes this by joining the
lines in the header, before doing the actual parsing.
Merge pull request #8 from Open-Xchange-Frontend/multiline_headers

add support for multiline string in headers
Recompile browser versions for #8.
Release v0.2.8