Upgrading v0.3

[Konstantin Veretennicov]

FYI,

Our migration went smooth and we've been using the upgraded Kallithea
instance for more than a week.

There are just 2 annoying regressions, which I reported to Bitbucket:
- https://bitbucket.org/conservancy/kallithea/issues/274/regression-pullrequest-gui-is-broken-after
- https://bitbucket.org/conservancy/kallithea/issues/275/regression-unicode-comments-fail-to-be

I made sure to reproduce them on a clean VM and clean install, to
exclude any upgrade-related effects.

I may have to look into performance also, as I see some abnormal
pull/push times from build agents (could be due to switch from the old
default 5-thread config to the new default 1-thread, or something else
entirely, even not Kallithea-related). Apart from that it runs pretty
well.

--
Kind regards,
Konstantin